A bright person can pick up a new language or framework in a few days or less, but it will take some time working in that ecosystem before they're really writing natural and idiomatic code. All other things being equal, I would prefer to hire someone who has experience in the same stack.
So, when it's time to move to a different stack, do you train your old team or can them? Or worse, relegate them to only maintaining the old stuff until the new stuff is in production?
If you don't move to a new stack, how's your retention?
