Wow best summary I've seen yet. For the most part it describes the situation on the ground pretty accurately. I only have 2 comments for the whole long Drashah:
While it's true they that, for the most part, they won't throw out a Shliach from before '94 who says Yechi, the reality is that these days it would be extremely difficult for a vocal Meshichist to find "official" Shlichus. The overwhelming majority of Head Shluchim are not Meshichist and would not hire someone who will say Yechi. Which is the reason why the overwhelming majority of "unofficial" Shluchim are Meshichist (the remaining minority are mostly Shluchim who were brought down as official Shluchim, got into a disagreement with their head Shliach and got fired but didn't want to leave their posts).
AFAIK there was only one time (12 Tamuz 5710, a few months after the Frierdiker Rebbe passed away) where The Rebbe referred to the Frierdiker Rebbe as "Der Rebbe Zohl Gezunt Zein". Though if you look at the Sichah of Rosh Chodesh Sivan 5710 you can see the background to that statement and there The Rebbe qualified it by explaining that he's talking about Ruchniyusdike health. In writing The Rebbe ALWAYS reffered to the Frierdker Rebbe with the title זצוקללה"ה נבג"ם זי"ע.
I guess we can all be thankful you decided NOT to be Ma'arich 
let me try address a few of your points:
The reason why most Shluchim seem to be more "anti" inclined, is simply because it's a lot easier to take that approach when dealing with outsiders, it's hard to mix spiritual feelings into something physical and practical, you can't tell a non religious Jew that you met that The Rebbe is still alive, he'll look at you like nuts, he watched CNN in 1994 and saw the funeral! but the community of CH is probably more "mishechist" inclined, they lived with the Rebbe and saw him on a daily basis and we all heard the Rebbe say clearly that this is the last generation of Golus and the first generation of Geula. Being on Shlichus, not saying Yechi for the practical reasons will eventually rub off on your own belief and your kids as well, that likely why most shluchim are more 'anti' what else do you tell your balebatim when you host a farbrengen on gimel tamuz?
As far as the Rebbe saying Shlit"a on the Frierdiker Rebbe, there are a few times where the Rebbe said it clearly, Simchas Torah 5711 (Toras Menachem Hisvaaduyos 5710(or maybe 5711) page 52, Parshas Vayakhel and Purim 5711, Toras Menachem Hisvaaduyos 5711 vol 1 page 274 and 327. and a few other places. Also in 5752 when the Rebbe had a yechidus with Mordechai Eliyahu, the Rebbe referred to the Frierdiker Rebbe with Shlit"a, it wasn't just once. The time you mentioned is when a chosid wrote that in to the Rebbe and the Rebbe said "bemes neheneisi" Toras Menachem Hisvaaduyos 5710 page 83.
Another time the Rebbe dismissed people saying nishmaso beginzei meromim, explaining that who are we to tell the Frierdiker Rebbe where he is, why are we separating ourselves from him? he's right here with us! why do we try send him away? (page 106). I don't believe the Rebbe ALWAYS referred to the Frierdiker Rebbe with זצוקללה"ה נבג"ם זי"ע, defintely many times but I wouldn't jump to write always in caps!
I got these page numbers from a compilation someone put together of all the sources for anything to do with Rebbe, Moshiach, Shlit"a etc. The book is only photocopies from seforim, there are no droshos explaining anything, it's just for the reader to see the sources and make his own decisions from there.
