My manager recently asked me to switch gears on the nature of my work. The core deliverables of our team, the bread-n-butter, are in domain, say X. I had been working in domain Y for the past year and a half, where my manager (& skip level) were invested and trying to expand the scope of our team.
However, a couple of people working on X recently left our team and so now my manager told me that we will decrease our efforts in Y, and will need me to work on X too. We won't completely be abandoning Y though, he said.
I have mixed emotions about this change. I am happy that I will now be involved in the core work of my team. I am also sad because I had just started to make an identity and started being recognised as the go-to-guy for domain Y. I feel the case for my promotion from mid-level to senior would also weaken with this change since I wouldn't have very solid contributions in any domain (i.e. no compound interest).
How should I make the most out of this situation?