Some of my favourite RPGs not yet mentioned in the first post so far were:
Might & Magic series esp. 3-9
Wizardry 6-8
Neverwinter Nights 1+2
Just to give an inspiration for discussion...
It seems there'd be great potential and working modular if spread work in chapters with a mindmap
If possible of course, as the most of them are some kind of open world.
Important for me would be the focus to do it as original as possible.