@Elzaïr
Creating a customized avatar has been a part of RPGs since the Elder Scrolls IV: Oblivion was released in 2006
It was already the case in D&D games by Wizard of the Coast and Bioware (Baldur's gate, released in 1998 in US)
Very, very interesting idea, as I planned myself to add such feature into my project.
About the softwares you quoted:
Make Human;
I started by use this one, but as I looked for the most realistic characters possible, I gave up few days later. The pro side is that yes, more easy to use.
Manuel Bastioni Labs:
True , not that easy to understand how it works but really precise shapes, without talking that the generated characters are really customizable in any way, not the case with MakeHuman. Also, Manuel's work is open source.
About the licenses: Well, the only thing Manuel asks is to credit him, even into a commercial project, not a big deal in my opinion.
Edit: Maybe you could contact Manuel Bastioni himself, he opened a topic about his labs on Blender Artists
I'm curious to see how all of this could work , as I'm not a coder and I could learn a lot of things.
Once gain, very cool idea