> Many of the hardest problems in computer science will become tractable with quantum computers of sufficient size.

I would say some, not many. Many of the hardest problems are NP Complete, and quantum computers are not expected to help in solving those.

> Question: when the D-Wave was first announced, people were saying it wasn’t a “real” quantum computer, but I can’t remember why. Is that still the case for these models?

It’s not a general quantum computer, so you can’t put e.g. Shor’s algorithm on it.