@User We are hoping to have a bunch of pins/pads dedicated to being replaceable with custom versions

Please can some of these be in the outer row of balls so that we can have microstrip traces on the PCB go straight into the ball with no vias, with the signal going through only a very short redistribution trace straight into a part of silicon where we can put RF circuitry (not halfway across the chip). Sorry to be greedy, but maybe it's better to ask now than later!

I second Chris's request. We need a highly controllable signal path for our analog inputs.