There are all sorts of considerations that have to be taken into account by any smartphone user who wishes to access their data on the move and it is not actually resident on their phone, some are:-
1. Access, wireless or whatever being available and not too many users in the vicinity.
2. The cost. Do you have an unlimited data package, pay as you go or whatever.
3. Do you really want to muck about with what you have on Ancestry on such a small screen. Fine if you have an ipad.
I have an iPhone, it would be nice to an iPad but I can't really see it fitting into my overall computer usage and I have in any event blown a lot of money on an iMac and MacBook Pro recently as I moved away from Windows.
I carry my database around with me. I use GedView which manages my 98,000+ database admirably, but its function, although you can edit etc is primarily a reference point and to show anyone who asks me, if I am not in full genealogy mode with laptop where they fit it. There have been request for an Android version of GedView but it simply does not make economic sense at present especially if you offer proper support.
I think that a lot of people would consider that any money available in Ancestry for programming would be better spent on improving the stability of FTM/FTMM