I don't know the weakest hardware yet, the project is still pretty young! But I am shooting for a 64-bit processor as the target. It seems a good midpoint between luddism and modern hardware, and I do want to experiment with multithreading later on. Right now I'm learning the hard way why I should've been doing screen edge plane clipping all this time, once I get that squared away I'll focus on more fully implementing the gltf importer and getting ready to create entities.
Update: implemented proper frustum culling and added depth fog and I gotta say, it's pretty gorgeous so far! (I might be procrastinating on setting up a texture bank so objects can look different lol) It took a bit to realize that anything relying on actual distance from the camera needs to have those distances set up in view space, before projection, because the depth buffer is non-linear (floating point numbers are more densely packed near zero than one)
overall, I like it, I think it has character