Sorry, but if you asked any meshichist if they would accept R' Shach as moshiach if he were chosen they would all say yes in a heartbeat. Sure they may want to clarify things with Eliyahu, but that wouldn't hinder them.
Thus nobody truly believes that the Rebbe and only the Rebbe can be moshiach. And refusing to daven in such a person's shul or eating their food just because of that belief is more foolish IMHO than believing that a holy and learned person to be a strong candidate of being moshiach. There is nothing halachikly wrong with that belief.
you're speaking a very moderate chabbad ideology over here on the forums, but i and many others from our experiences have found otherwise. just because they would "accept" who eliyahu names (lmao btw, that you think there's a need to say that), does not mean they don't fully believe at this point that the rebbe IS meshiach. is, not, could be. that's a meshichist. there are many of them. you claim they're an "extremist" element, but it seems like these "extremists" are all over the chabad enclaves, including 770, crown heights, cfar chabad etc. and there is a lot wrong with that belief. and it possibly borders on kfira. and it certainly entitles one to not be interested on relying on such people for the food he puts in his mouth.
if you really believe as you say on this thread, which is questionable, then you don't fall into that group. good for you. but don't sit here playing holier than thou about "castigating hundreds of thousands....," when there are so many who do hold that way. and on top of that, you don't for a second hesitate to stereotype and castigate litvoks, who by the way, number a lot more than chabadskers. so stop the preaching.
and there is no other chasiddus that espouses such beliefs. if you claim otherwise, show a source.
And I hope you don't drink any Bartenura wine btw
sure don't. enjoy it.