Exactly this. I have a current specialism within a fairly specialised field, but this leaves me plenty of bandwidth to move within the field in the short term.

Exactly this. I have a current specialism within a fairly specialised field, but this leaves me plenty of bandwidth to move within the field in the short term. My background is loosely related but has given me a set of core skills which I can draw on where I see other people being employed as specialists. I try to maintain my core skills in other areas to the extent that I can commoditise them for my own purposes if needed, even though I have no interest in actually pursuing 'excellence' in them. When I first started down my specialism a number of years ago my expectation was that my previous background would become irrelevant as it felt like quite a big pivot. I was (and remain) surprised at just how wrong I was - having additional background skills that aren't directly related makes me more valuable.