To begin with, everything you have pointed out is spot on and I see no way to improve on it.
As to Clovis the Riparian, the earliest place I ever saw him was in Ancestral Roots who cited an article in NEGHR which in turn cited J. Depoin: "Grandes Figures Monocales au Temps Merovingiens"in Revvue Mabillon, XI (1921). The line was then worked over a little by David Kelley (who did not look at the first two generations but was concerned with the generations between Munderic and Arnulf) and later the same area was further adjusted by Settipani in L'apport de l'onomastique dans l'etude des genealogies carolingiennes in Onomastique et Parente Dans L'Occident Medieval (Kelley agreed to some of his adjustments and kept an open mind about others I think). Acknowledging that the line was first laid out by Depoin, Settipani then went back and reconstructed it but notably the line started in his article with Sigibert the Lame andd he refers to no ancestor earlier than that (as I think he would have done had he known the name of one or even the probable name of one). There is a strong sense that Clovis first wife (Theoderic was not Chlotilde'S son) was probably a daughter of the leader of the Ripuarians and Sigibert's sister. Hence Clovis and Sigibert are referred to as kinsmen by Gregory, purportedly quoting Clovis himself.
"'Audite, quid contingerit. Dum ego', inquid, 'per Scaldem fluvium navigarem', Chlodericus, filius parentis mei, patrem suum insequebatur, verbo ferens, quod ego eum interficere vellim." Reader's of the Penguin Gregory see the word brother and may interpret it as "brother king" meaning no more than fellow but as Gregory has Clovis say the words "parentis mei" and since it is unlikely in this instance he had the text of Clovis utterance verbatim (he will have heard it from a retainer or lady in waiting of Queen Clothilde who spent her last years at Tours before Gregory became Bishop) it means that in fact Gregory regarded them as relatives. I think here however, "parentis" includes in-laws and is similar to our "kin". However, in classical latin it does suggest a blood relationship and that is what Depoin decided it was (If Depoin is right it seems more likely to me that Basina of Thuringia might have been the aunt of Sigebert but again there is no way to know that and in the best latin sense parentis should suggest that Sigibert was Childerich's brother which - since there were two independent kingdoms - Salic and Ripuarian - whose particularity was so intense that the Merovingians had to place a separate king on the Austrasian throne and that king took names alliterative with the old Ripuarian line) On balance I think Clovis married into the Ripuarians. Indeed this may have been the initial source of his power. Note that the Salians were settled in the low country. Syagrius son of Aegidius, the former commander of Clovis father Childerich had ccontrol of the area after the empire collapsed. When Childerich died Clovis will have needed some backing to attack Syagrius and it most probably came from his in-laws the Ripuarians.
Thus when Clovis had Sigibert's son, Chloderic the Parricide killed, he gave the impression of someone avenging family honor and remembering an old debt and hospitailty. Were it not for Gregory spilling the beans that might well be how it would have seemed for ever after (and Gregory is telling the story near a century later).
As a subtext to this, it is not clear how Chlotilde (Gregory's likely source through her surviving retainers) for inside information on Clovis court regarded the affair. It appears that the Burgundian Royal House had close blood ties with the Ripuarian Franks (Aregund and Ingund were said to be daughters of a Chlodomir Frankish King of Works. Since they were born ca 510-520 this person would have been about Chloderic the Parricide's age.
One gets the sense from their names and the names of thier children that they had strong blood ties to the Burgundians and all the stories among the overentusiastic to the contrary notwithstanding, though this story is likely to have been late, it trumps the "They were daughters of Baderic King of the Thuringians" school of "thought" (If they were that closely related to Radegonde, Gregory would never have let us hear the end of it). ASsuming arguendo that they were Ripuarian Franks with (as only seems logical - since the Burgundian Kingdom had been founded at Worms) strong Burgundian ties - The Thuringians, Ripuarians, Salii and Burgundians were intermarried and all tied by marriage to the family of Theodoric the Ostrogoth in Italy, the story of the temptation, subversion and then murder of Chloderic by Clovis, true or not, may have been the fruit of another of Chlothilde's resentments (Her husband's family in addition to avenging her had the tendency to obliterate all those she might have cherished). Hence Gregory may have outed Clovis, a man he otherwise tried to paint as a "second Constantine".
Whoever the father of Sigibert was he was likely quite powerful (And may well have been a son of Theodemer - interesting how that "Gothic" name precedes the Ostrogoths into the area by almost a century - but it is authentic - Gregory cites it from a much older historian)
Depoin may have seen notices of "kings" with these names in ancient authors, saints lives and the like and strung them together assuming an hereditary succession - not that sound an assumption in the early 5th century but which of us are not driven to do this at times by the dearth of sound records (And Gregory, well informed as he was and living near the time probably had less access to good records than Depoin. Thank Heavens and Gutenburg. If I can ever get my hands on the Revue Mabillon article I will post any cites for these two mystery generations here. For the moment, I assume, as apparently Settipani does in Onomastique et Parente and Kelly would if asked I am sure that these first two generations are not reliable (I admit it did not cross my mind to ask him on those occasions when I might have).
One interesting thing that comes out of all of this is that at the time of the fall of Syagrius (who had inherited a sort of Frankish hegemony from his father Aegidus) you had three Frankish kings in Nuestria, Clovis, two Ripuarian kings (Sigibert or his father and Chlodomer I of Rhiems) and three Thuringian Kings (Not to mention 3 Burgundian Kings and enough Saxon and Frisian Kings on the continent and in Britain to fill an auditorium) Tremendously fragmented. Most of Clovis life was spent unifying the Franks in and out of the old Empire. Defeating the Goths and Alemanni were sort of a satisfying final act.
Anyway, in conclusion, I would not accord any significance to Clovis the Riparian or Childebert. Although I would not accuse Depoin of inventing them from whole cloth (many others have done such things but I think not him) but until we know where he found these names, nothing really can be assumed about them. What Settipani says is true (about "maybe" the Ripuarians and Salii sprang from Theodemer around 400 though there is no reason it "need" be so) but Settipani says (as you point out) nothing about Clovis and Childebert, Kelly says nothing about them and Gregory says nothing about them and that is pretty significant. I would, for the time being, start the line with Sigibert.