So basically, superdense material? Weight doesn't change how fast something falls IRL, but if you made something so heavy in TPT that it fell faster, it would cause issues with the game's pressure grid (eg, massive superpowerful explosions).

...Or, it would just fall through everything and disappear off the screen. If you made an element manually calculate on every frame how far it could possibly fall, this could easily work, but that would make it totally immune to pressure (imagine fog or most solids.)

The idea of falling instantly is the coolest part of this. Moving points of gravity however would me less useful, since gravity doesn't update very fast at all with anything more than a few dozen pixels.