SIR is to the subway what Canadian Football is to American Football. Close. Similar. If you've never even heard of the CFL but I showed you some footage, you'd know it's gridiron football.
That being said,.. Currently the SIR has 15 trains... and they are getting 15 trains. They don't need all 15 to provide service since ideally, some will be undergoing inspection, and some will be in reserve, to the point having to take a bad car out of a consist and add in a replacement is more effort than to just say "just park that set and go get a different one".
So, in theory, the could use an open gangway or at the very least, a permanently coupled set.