> How much time would it take for a smart, competent and self motivated person to get up to speed on this new but related field?

Hiring someone willing to learn a new field filters for generalists and people who need jobs. Neither of those qualities are bad.

Specialists, or people in love with a stack, don't want to use 'some other tech'. As a senior, I pick the stack, because I have an idea where the industry's at and what's best for the type of software I'm experienced with making.

These hidden filters are interesting.