The way it works with standard-issue cis equipment or anal penetration (and I only have first-hand experience with the latter) is that muscles, not mucosa are responsible for tightness. As long as those muscles are stretched without tearing and scarring (very bad!) looseness is temporary. No more than a few minutes, typically less than one, for even the smooth muscle to return to resting dimensions.
What does change, quite noticeably, is one's ability to relax and take - hmm, not
too much detail... Dilators intimidate me not by size (

pictures would be inappropriate, may this express mild derision

) but the fact they're made of hard plastic. (
Mad respect there. Would. Not. Want.)
If the construction technique is good enough, capacity without looseness is certainly possible. In theory. I don't know about specific techniques, and once the dilators get to the size of soda cans...
I think I'll hide in the corner and whimper. Just imagining.