Minetest runs on the Irrlicht engine, which actually has an OpenGL ES renderer as an option. So it is possible for it to run on the N900 (in fact, the Pandora people have gotten it running on their device (but I tried running the Pandora version on the N900 and failed). I briefly attempted porting it myself, using the patched version of Irrlicht that Cloudef on the Pandora forums made here, but it seems as if the N900 initializes an OpenGL surface in a different manner from Pandora, so it does not work (this result I came to after many hours of editing include files and commenting out random bits of code so that it would even compile in the Maemo SDK). After a brief attempt at copy-pasting the EGL surface initialization code from the sample Maemo OpenGL ES app, I gave up (I'm not really a coder).

tl;dr The N900 has all the libraries (in the repos right now, actually(!)), except for the 3D engine it runs on, Irrlicht. It's completely possible to port that to N900, we just need someone with knowledge of how OpenGL ES surface initialization works on N900 to fix that.