I've never heard anyone talk about annexing Ireland or making Ireland part of the UK again (aren't those two things synonymous?). I have heard Brits complaining about having to use non-EU lanes at airports, but that has nothing to do with Ireland - it's a completely predictable and negative consequence for Britons of a very divisive and unpopular political decision. I promise you that few people in England care either way what happens to Ireland, or at least no more than we care about, say, Sweden or any other near-neighbour who we're not at war with.
Hell, even Northern Ireland doesn't get much attention here, and that's part of our country. Most young Brits today are completely uneducated about the Troubles (although they've heard of it) and probably can't name a single Northern Irish politician. Brexit was a welcome reminder to the rest of us that Northern Ireland exists; our current dilemma is caused by the necessity of reconciling two utterly incompatible goals - keeping Northern Ireland within the same system as the UK while maintaining an open land border with an EU country. (The irreconcilability of these goals was pointed out by many people before the referendum, so I guess we can't say we weren't warned.)
> the "solid majority" in NI isn't so solid anymore.
Yep, I'm aware of that, and Brexit has definitely eroded that majority. Irish unification (as foretold by Star Trek) within my lifetime seems increasingly likely. Good for them - it's for the people of Northern Ireland to decide for themselves and I truly don't care which way they decide.