I believe that a layman's explanation is that BIP91 facilitates (or forces) the locking in and activation of segwit, which locking in adn activation of segwit process will take place in August.
BIP91 also causes some attention to a possible 2mb blocksize limit increase through a hardfork - however, the language of BIP91 does not seem to mandate those further steps regarding 2mb increase or the hardfork.
So the more important thing about BIP91 seems to be providing a vehicle or a channel to activate segwit - which also nullifies the activation of BIP148 (User Activated Soft Fork) that would have gone into effect on 8/1.
Can anyone say more than that would be more concrete than speculation?
Segwit2x does not have a valid BIP. Miners were meant to signal their intent to fork with segwit2x by adding NYA to their coinbase.
BIP91 was proposed by James Hilliard as a way of making segwit2x compatible with BIP141 (the original core segwit activation). Thus it does not have anything to do with the 2x hard fork component in the future. The only thing that says miners are for both is the presence of NYA in their coinbase, which doesn't even activate anything in particular, it's just a comment, along with the continued signalling on bit 4. You can see why the hard fork is precarious in light of this.
Thanks for that further clarification, and some times it feels like we are beating a dead horse with some of these matters and the repetition of various themes.
And, sometimes I cannot help myself by using denigrating language to refer to some of these big blocker folks - but the fact of the matter is that they cause their own ambiguity seemingly on purpose and then try to take advantage of the ambiguity. They fail and refuse to follow various formal practices or to follow through in such a way to cause clear and unambiguous mechanisms. They likely realize that the more clear they make it or the more formal they make it, then they will lose a large number of followers because they are missing mechanism to trigger or to formally achieve their goals - so they resort to various passive aggressive tactics and reliances on nuances, rather than following established systems and protocol... or otherwise proposing reasonable and acceptable ways to tweek standards and protocols.. so yeah, I see what you are saying with the lack of triggering mechanisms that seems to cause quite a bit of their own problems and ambiguities.