I don't disagree with anything you've said. However , i've
found it a lot easier to make the final frequency adjustments
in a superhet since it can be done at a lower frequency.
Trying to sync up at 915 is more challenging than at 455 khz,
obviously. And for systems like FSK and SSB, you gotta
do it somewhere..... And with FM, since the beat formed
by the carrier depends on the modulation index of the
received signal, getting rid of it can be squirrelly.....

You mentioned FM. I have a general question about the Tayloe mixer. Is it
possible to receive NBFM or FSK from VHF with it? I'm a little lost in the
question how to use the for outgoing phases or I/Q to demodulate FM. All I
found on the Net was doing shortwave SSB demodulation.
Are there other analog switches going higher than the mentioned 70MHz for
FST3253 or 74HC4066? Perhaps video switches? What is better: Tayloe 4-phases
or a switched mixer with one output only? In the latter case I would need a
conventional IF filter after the switching mixer?

If I need a DSP at the baseband doing math with the phases or I/Q I would
think of an www.wavefrontsemi.com DSP AL3101/2CG DSP-1K will suffice? Wolud
it suffice? It is a little simple DSP mainly for doing FIR - but FAST and
with 24-bits including audio AD converters ip to 50KHz. The DSP runs with
50MHz up to 1000 instructions long until it repeats the prog. The nice think
is a very low pin-count package and cheap too.

There is maybe a middle way with a device like the www.cypress.com PSoC
family of mixed-mode Microcontroller with programmable analog cells. There
even exists a PSoC app note describing a heterodyne FSK receiver for 130KHz.

Maybe a www.microchip.com dsPIC is better?

Would it better having the IF not at zero but at a usually higher IF, say
25KHz (remember the NFBM!)?

regards -
Henry