So I would assume 3D wise pretty much anything goes aside from animation (anything requiring joints etc) and probably high poly count stuff (don't know a lot about 3D).

The only problems so far with demo's are with the included pngimage which is solved by removing that folder, PNG is support directly in Delphi for some time now (I think it's even the same guy that implemented it), and with
the BASS implementation (the included .pas) file had quite a few errors but I just removed sound from the game so I could test it rather than mess about with it.

I have always used Delphi as I like the IDE although I don't use a lot of it's features, never tried Lazarus or others.