That Idea is super AMAZING, but so dam OLD, even when DBO was in development they had it, but, why didnt come out?
A couple of problems.
1.- Every head from the characater customization, must have a concordant 2nd phase, 3th, and 4th. It means that u will need 4 more models for every head style u create, and remember every model need his unique texture format and configuration even if it is the same texture for every model.
2.- The 3rth Freeza transformation not only change the head, also the back torso of character, it means more models for every head, and more textures.
3.- Final freeza trasnformation changed all the bodytype, it means more models for each head type, and more textures again.
4.- Every frezza transformation had a diferent size, that aint much of a problem, but as u can figure it out now, it will need more work, to make it look accurate.
5.- Freeza Home PLanet is a technological advaced planet, it means tha the initial map will need more buildings and modeled things, that any other map, yea it will be too much work again, its esier and cheaper to create Korins map than Freezza's map.
6.-All Classes have the same feet here, all humanoid value system whit cloths, thats why they didnt creat Cell either, but freezzas feat are only 3 Fingers, pretty unique, the gear will be another issue to deal whit it, cuz ofcourse frezza dont use cloths. They need more time to came up whit new ideas of how gears are goona fit whit freeza's race, (starting whit the feet)
7.- Once freeza is in final form there is no other transformation, the 100% freeza its kind of a technique, more like Kaioken.
so this classe will break the skill tree structure, that all the other classes already have.
This are just the main Issues I identify in the very first 5 minutes, im pretty sure they are a lot much more.
Your Idea is pretty much, the best one there is for DBO, but just aint gonna happend. A new Dragon Ball game will come out first before this happend to DBO.
Conclusion:
Making Bu Race, instead of Frezza race was cheaper, thats why freeza isnt playable in DBO
Thumbs up bro
pls dont feel blue about it, I didnt meant to be negative.