(x) It will stop spam for two weeks and then we'll be stuck with it PoW hardness...

  (x) It will stop spam for two weeks and then we'll be stuck with it

PoW hardness can be controlled with a parameter.

  (x) Users of email will not put up with it

It is optional (no one is forced to use it).

  (x) Microsoft will not put up with it

Microsoft will put up eventually if the majority uses it.

  (x) Public reluctance to accept weird new forms of money

There is no new form of money involved.