Bitcoin XT is the only viable implementation of BIP 101
It is not. Any miner can make a copy of XT and remove the patches that he objects to. Or make a copy of Core and add only those XT patches that implement vote-triggered 8MB limit.
If you are not a miner, you (or any programmer you trust) can make a copy of Core, simply raise the size limit to 8 MB, and start running that version any time before the fork actually happens.
I'm not sure the masses of adopters are gonna do this / or even know-care about the possibility. Vanilla XT is the intended norm.
I'm part of the Any miner people, I'll just use XT I can write a script but compiling code that's complicated stuff, I'll leave that to the developers.
There must be developers who are nothing to do with core/XT in this community who are capable of making those modifications and compiling a wallet. If some third party developers offered a third choice then more people might adopt that than the alternatives offered by core/XT. Professor Stolfi must be capable of doing the job if nobody else is prepared to do it, or capable of doing it.
There's actually nothing wrong with that. The nature of open source means that you can fork the code and change it as you wish. As long as you can get a majority to follow you that is.
Anyway, I dont think we are lacking choice here, with 2 versions of core and an unknown number of XT;s knocking about. Its consensus thats needed, and as the blockstream side have gone to great lengths to illustrate - that is not going to happen.