Your question is a very big one and I doubt that any software product even understands its own internal s to GEDCOM very well. Also you will have problems with which version of GEDCOM to support v5.5 or v5.5.1 or some other older version. Then of course there is all of the various custom tags that support things that either are not support well by GEDCOM or the software ignores a GEDCOM tag but uses there own custom tag.
You would be better served to sell a subscription to an online sight with good security and be the admin for any updates.
As a long time GEDCOM user I have never been happy with the way every software program miss uses GEDCOM.
Check out the "bettergedcom" and FHISO organization and see from them how hard it is to interchange information. I support their work, but the project will be a large one.
I could go on and on but I said these things here often.