The 2015 force touch never actually moved nor created a gap when pressed down hard. I am afraid dust, hair or small crumbs may get stuck in there..Why would it actually go down or create an opening on the edges?
I have a 2016. I can't see any gaps opening up in mine. I wasn't even aware that it really moved at all. Whatever movement I see in mine is very minimal... not enough for me to worry about contaiminants getting into the inner body.
Besides that, I do think the concern with dust is... overblown. (Sorry, that word always makes people angry.)
While I do believe that dust can be a problem, I don't believe iFixit's conclusion that a single grain of dust will kill a key on a
normal butterfly keyboard. I believe that the ones that could be so easily jammed are actually defective and probably shouldn't have passed inspection. My 2016 MBP is a custom build placed in the initial batch of pre-orders in the winter of 2015. I have a machine from one of the most notorious batches. If dust can kill a key on any butterfly keyboard, I shouldn't have a single key left because I'm sure there is all sorts of junk a lot worse than dust in mine. I'd be embarrased to let someone inspect the inside of my keyboard.
Don't be a slob, but don't worry excessively about dust either.