Without reading any of the specific posts and without any disrespect intended towards anyone (here or there ) when I see titles like "Challenges facing Buddhism in the West" or "Challenges facing Buddhism in the East" or "Challenges facing Buddhism in Today's Age" or "Challenges facing Buddhism Tomorrow" etc I admit I have never really seen these extraneous items as challenges.
Buddhism, true Buddhism is alive, everpresent and to use another trite phrase, omnipresent. Were it so, then it is already all around, as the Buddha suggested. The more visible elements and banners like monks and nuns and sutras and temples are one facet, but there is also the other, some of the real work of the Dhamma everywhere.
I guess if I had to vote, I would say more of the challenge facing Buddhism is that we are not are able to actualise what the Buddha taught for us, and thus actualise Buddhism, which also includes eventually seeing that we cannot be bound even by the constrains of formal Buddhism. In this way how could Buddhism ever be challenged? What feels challenged at the moment is only 'me'.
Were this all so, then more of the superficial elements around location and timing lose its force: they aren't not pertinent, but I think at least, they lose their force and focal point as 'the challenge.'
Not saying I'm right or wrong, but the title just got my thoughts going. Best wishes.