Hi Sameer,
I've known a few FICO Consultants that moved to BPC.
FI and BPC are related as Finance user to budgeting and planning.
While FI is part of ECC, BPC on the other hand is based on BW as back-end, with Front-end web-based interface and EPM-Add on for Excel for data maintainence.
The Idea of BPC is to load data from Sources (be it ECC, another BPC, BCS, BW or even 3rd party) as actual data, and then user will plan budget by referencing to the Actual data (together with Forex calculation etc)
If you have experience in FI as support, IMHO, I think it's better if you sit for FI cert, or try study for SIMPLE FINANCE (S4/HANA) a.k.a the new might-replace-the-current-SAP-FI in the future.
But of course, if you want to go for BPC instead of FI cert, that's not a bad choice too, but just make sure you know what is BPC, before you step into it.