Re: OK, I'll bite
The obvious solution for Spectre would be to add some bits of the pointer to the head of the page table into the branch history table indices
That only helps with one of the two Spectre variants demonstrated in the original paper, and in that paper the authors point to other side channels which are probably also usable for Spectre attacks (e.g. ALU contention). Blinding the BTB would be a bandaid.
As anyone with a crypto background knows, it's really hard to reduce all your side channels to the point where they leak information too slowly to feasibly exploit. Paul Kocher showed us that more than 20 years ago, a mere 7 years after the DEC branch-prediction patent was granted.
 Sticking plaster, for CPUs in the Commonwealth.