The single coil latching relays often get away with less power, but the driving with bipolar pulses is a bit more complicated. With half the coils it is still not that bad and there is a solution with N+1 CMOS drivers for N relais.
The PV drivers for a MOSFET gate can get away with a little less current. I get away with some 2 mA (2.2 K series resistor with 5 V supply). If needed as a pair, 2 diodes may be wired in series. The voltage at the PV driver is not the full 3.3 V, more like 1.2 V for an IR diode, though a few types may use 2 diodes in series internally. The resistor can be more with the control part.
The balance between heat and leakage is indeed a bit tricky. Usually nV accuracy is not needed in combination with very high resistance and the MOSFETs are usually not super high isolation anyway. So the MOSFET based scanner would naturally have a bit more leakage, especially with many channels. For the heat of the PV drivers much would be about spreading it out / linking the different channels, as usually 1 channel is active at any time, just the position changes. A constant heat source is a smaller problem than one that is moving around.
In many cases one would not need that many channels, at least not the high precision ones. With slightly leaky switches more channels also come with a downside. At least from my experiance one often has a combination of a few precision channels and than sometimes quite a few additional lower grade signals (e.g. temperature, supplies,...) to monitor. It can there make sense to have 2 (or even more) separate meters and scanners. The sometimes tricky point is combining the data.