I'm a senior dev who currently found himself working with C. On one hand I love it as it is familiar to me and I "get" it. OTOH I'm afraid it is regressing my future prospects as many consider it obsolete language and I'm in a market dominated by web dev and java enterprise.
So I'm thinking of investing in learning a more contemporary tech stack to stay relevant and employable. Doing mostly systems work (performance matters which is why we write in C) I was thinking maybe rust is a natural step for me but then again I worry that it won't get much traction in companies (lots of pushback from devs and management invested in older stacks, learning curve, not time tested etc).
Anyway. The real question is how you decide where to invest your time/energy next? I don't know of any method to attack this problem other than let the circumstances choose for me.