"Wusti, on what basis do you claim that Jeremy Corbyn, who was resoundingly ELECTED as the leader of the Labour Party, and who has DOUBLED the membership of the party, is "unelectable"?"
Sorry, but growth of party membership from less than 0.3% of the national population to a somewhat over 0.6%, even when its combined with relative popularity among that 0.6%, falls short of electability on its own.
Besides this, what new supporters is Corbyn going to bring in to overcome the Conservatives? Is he going to increase turnout of Labour supporters who haven't voted previously (plausible, but is it sufficient?) or by siphoning off support from the Greens (don't know how likely that is)? Or is he going get soft Tory supporters to come over to him (I have trouble imagining that)? Or is he going to bank on a swath of Tory supporters staying home or deserting to UKIP (again, I have trouble imagining those scenarios in the present environment)?
I don't think the lack of support among MPs necessarily makes him unelectable or that people care about internal party wrangling nearly as much as the media does. In fact, I rather suspect they don't care about it much at all during the off-season away from elections. If Corbyn survives this challenge, the party will either split or heal itself (my money would be on the latter). However, if Corbyn does survive and then later manages to form government with a PLP of the sort that he's facing now, he may find himself being reminded of his own history of dissent -- only from the other side of the leadership divide.