I actually love the way the game "Kenshi" does it. But those are not renders, it's a 3D engine. You can pick up a really, really starving, skinny NPC and with time, food and workout have a beefed up hulk full of muscles. Both male and female. To make that in MoR, it would require a huge amount of work adding all the different render varieties.
Come to think of it, even though Kenshi has "older" graphics now (I still love the game) the body engine is remarkable. A mix of MoR gameplay with some sort of real time 3D graphics would be dope! One good thing about Kenshi is that it runs just fine on less powerful computers for a a very complex real time fully 3D open world game. My cheapish PC from 5 years ago runs Kenshi great.
Another game that comes to mind in Porn Empire (early access at itch). The game does not allow for body changes, but the amount of different body styles available could easily be used to "grow". In the game you get skinny to plumb ladies all across the board. It's all 2D but it's nice done.
One thing I would like in MoR is to have the head maid (I think head housekeeper would be more accurate) try to keep certain aspects in check, like arranging food portions (maybe have body fat goals for all or even for each girl. Having to manually check body fat and adjust food for each girl is a pain (especially with the menus like they are). Even having NPCs workout on their own (passive) would be good. Like a daily passive workout that could slightly improve physical and other skills too.. Yoga lesson in the morning for brain focus, relaxation and body toning? LOL
Even a simple "excel style" list of NPCs and attributes would be a good addition.
It's all nice and good when you have 20 NPCs, but once you get to 40, 50 and upwards it's a real drag.