It's actually a funny idea if you think about it.
So mass is getting heavier but one has to ask in reference to what is it getting heavier?
We need the universe connected to something that isn't in the universe which is pulling those things in the universe progressively harder and giving them more mass.
Note that is a very different proposition to dark matter which is still in the universe just not interacting very much with matter but reacting with itself.
It would actually make more sense to reverse the above argument and say the area outside the universe is pushing back on matter stronger and stronger because at least outside the universe is already that outside the universe.
Hmmmmm lets call it non universe resistance and it's increasing ... wonder if I can get published
