For the frequency range, they would be switching in/out a different capacitor ... for the gate time, they would select between the outputs of 2 or 3 decade counters.
The auto-ranging etc. are indeed the kinds of things I was thinking of adding ... "great minds think alike" ... ![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
Also wondering how the "on" resistance would influence things.
Selecting GATE signals could be done with either an analog switch or a digital MUX.
Or, you could generate the gate using the MCU timers.
If you have the MCU, you can also use a simple external gated binary counter to prescale a higher Fin to a more modest rate the MCU can count itself.
If you have reciprocal maths working, that counter becomes a simple multiplier.
If you want to measure pulse widths, the hardware gets a bit more complex.
Something like input AC or DC coupling, is a natural for a mechanical switch, and tougher for an analog switch.
My PM6672 reciprocal counter has a knob for nominal gate time, and a knob for input slicing level when DC coupled. which becomes gain when AC coupled.
How much of this already exists in 'working hardware' ?