> "FPGAs reconfigured during program execution to speed up hot paths"
The IEEE conference on Field-Programmable Custom Computing Machines (https://www.fccm.org/) is in its 34th year, to give you an idea of how old that idea is. The answer to your question is both 1 and 2 and also 3. that FPGAs have rather poor efficiency, both in terms of cost and performance, so it's not worthwhile outside of a few niches.
The IEEE conference on Field-Programmable Custom Computing Machines (https://www.fccm.org/) is in its 34th year, to give you an idea of how old that idea is. The answer to your question is both 1 and 2 and also 3. that FPGAs have rather poor efficiency, both in terms of cost and performance, so it's not worthwhile outside of a few niches.