Butt expansion, probably not. I don't hate it, but it's not really my thing, and when my creative engine is fueled entirely by passion, that means I can't produce enough motivation to do it. As for lactation, in the lore, sure, but not really as a gameplay mechanic. Liquids are... nope, and I'm not actually using any currencies other than boob size. Trying to balance the milk quantity octupleing when the boob diameter doubles while also dealing with very real bit limits was a little too hard for me in Yuri, so I won't do it in GTF. There will, however, be boba.