The make and model of the inverter(s) and PV panels (and count), and of the service equipment, would be helpful in advising you.
1) The typical reason to do that is the "120%" rule which is one of the options for interconnecting the PV inverter output on the load side of the service disconnect. It says if you put the interconnection breaker at the opposite end of a panel bus as the utility breaker, then the sum of the breakers (or rather, 125% of the inverter output current) can be up to 120% of the bus rating.
So with a 125A bus and 125A main, the inverter breaker could be at most 25A (or rather, the inverter could be at most 20A or 4.8 kW). Downsizing the main breaker to 100A allows a 50A inverter breaker (or rather, inverter current of at most 40A, or 9.6 kW).
2) Not familiar with Remote Metering Device or how it would help. Upgrading the panel bus rating would allow putting back a 125A main breaker (assuming the inverter output current is between 20A and 40A, so that the downsize was originally necessary). You could possibly switch to a line side connection of the PV (between the meter and the main breaker), but the feasibility of that depends on the specific service equipment. If that would require replacing the service panel, then you might as well put in a larger panel and perhaps stick with your load side connection. Lastly, depending on the system size and degradation of the PV array, there is a possibility that downsizing the PV inverter to be 20A would be feasible without reducing the energy production significantly.
Cheers, Wayne