Yes, saying it requires 3000 pics to redraw is just a gross estimation for implementing futa mechanic. Hidden cost is a thing in game development.
Dev has some ideas about adding futa elements, but I think there are two major game design concerns the game dev has to consider.
1. Dev has to decide how large the futa mechanic is. If it just settle it with a simple pp, then the futa gameplay experience wouldn't be that fun. Its either nothing, or an entirely new gameplay experience like DeepOne mechanic. If that's the case, making a new gameplay experience wouldn't be settled by just redrawing 20 dicks on Lona.
2. Dev has concerns about the theme of the game. If futa mechanic was added into the game, that means gay option would become openly available to the players. Dev might fear that some players might react negatively to the new futa mechanic. Therefore, the lack of confidence to implement it. Personally, I don't think it would affect the theme of the game that much, but this is a thing every devs would consider.
Code wise, I didn't research about how the game code works, but I don't think it's easy to disable vaginal option by just pressing a few buttons. Its a fact bug issues are hard to fix, and it tends to get worse as the game gets much more complicated.
Look, everyone would love to have Lona to JAM her Double Jointed Penises with Spiked Head into orkinds' tiny trembling anuses, until their asses were being completely DESTROYED.
I think the best chance to convince the dev to actually implement it is voicing the market demand via donating.
It ain't easy to draw juicy futa content like these.