Apple will announce a Developer Transition Kit at WWDC, which will
be available this summer. The DTK will use an A12Z (the current
iPad Pro SoC), inside a Mac mini chassis. Or, I think less likely,
an Apple TV chassis with added I/O.
I don’t think it will be a laptop: that would require full power
management to be implemented, would be more expensive, and would
result in battery life figures for semi-prototype hardware being
reported all over the press. That’s really not how Apple rolls.
Great post overall — I think Shanks is largely spot-on.