True, oldfags do indeed have the money factor on their side; teenagers rely on monthly allowances and young adults have plenty of financial obligation to fullfill with their measly pay. But it is precisely because of that, Bandai targeted oldfags on their higher price product in MGs and PGs because they can afford it. While sure if Bandai releases RG domdom or gouf or gyan, oldfags like us would buy it, but newfags wont. On the other hand, if Bandai releases stuff like seed or 00 or maybe even wing, it'll be more profitable since those show are newer in comparison and younger ppl could relate to it more + the attractive price range of RG line would equals to successful sales. Even oldfags like us would be drawn into getting these.

So from a mathematical standpoint:
a) old stuff like gyan: oldfags $$ + small% of newfags $$
b) newer stuff like seed: oldfags $$ + newfags $$

Base on these, its understandable why Bandai opted for option b. Of cuz there are exception to oldstuff. Things like rx78, zaku, etc are popular irregardless of age so those are made, but i wouldn't expect stuff like gyan or gerbera tetra to be made.

As for RG zeta, possible. But even in the MG form, its quite fragile, in RG it maybe worse though. I think generally, complex transformable design would not be release so fast. Maybe if they did, it could be swapping parts rather then full transformable. Can you imagine the horror and nightmare ppl would suffer from transforming things like Delta Plus, Ex-S, etc if those were made in RG. Easier transformation suits like Wing (just twist the waist) or Epyon (yoga style) could be done easily, so those maybe the 1st of transformable RG models.