I don't pretend to be a Corbyn expert, in fact I found out he'd won on this forum first. A good example, perhaps, of how jaded some of us are with the British political system.
The surge of people joining up is, though, quite interesting imho.
Ambrosia pointed out, quite correctly, that Labour got elected in '97 because the people were tired of the complacency of the Conservatives who thought they were an unbeatable force that could do whatever they wanted.
(I remember seeing the look on Portillo's face when his constituency results were given

and he realised that Democracy had won)
My unimportant guess is that what we are seeing here is similar.
People are very tired of same old same old.
Would he ever be P.M.? I doubt it, unfortunately.
But as leader of The Opposition he will, at least, prompt discussion and debate in The House. And that is the purpose of that place and is the job of The Opposition.
I'll keep an eye on BBC Parliament.
ETA: There are lots of UK members here and, believe it or not, even some of The Americans are interested in this stuff. There really should be a UK Politics sub forum rather than a general "everywhere else" one.