I don't know where to put this, but I found a video by GamingEngineer where he looked at his old games he made. And he made some FPS prototypes with 3D models, and I was wondering is it possible to make a Quake like game in Legacy GMS?
Possible yes(or others wouldn't have already done it). That said, like most projects it will be much easier on the newest GMS2 version. The issue where 3d is concerned under discussion with Gamemaker is more about the difficulty in general of working with 3d because the software is not built for 3d. It can be done but you have to code or acquire code for the missing stuff, like loading models, animation, etc... this applies to both old and new versions.