Sure, just do the Zeta SDR schematic in reverse, but like others have said you'd have to figure out the rest of the chain as well as a tone of filtering. I've transmitted with direct digital synth chips as well as rpitx which is literally bit-banging RF off of a pin on a raspberry pi with NTP sync even. Again, still had to do a lot of filtering, but with wsprrypi I was able to be heard one time in New Zealand from Ohio, USA without any amplification.
Naturally there needs to be filtering and some sort of analog frontend.
My main point was that mainstream rigs now do direct sampling, instead of zero-if or superhet with dsp IF.
And WSPR sure is magic, people do thousands of km with it off an rp2040 gpio pin.
I'm not sure this is what you have in mind as far as "mainstream" rigs or architecture, but the FTDX-101D main receiver is a "narrowband SDR" system, as Yaesu describes it. Signal is downconverted through an analog chain including a narrow crystal filter before it reaches the 18 bit A/D+FPGA. And yes, it does perform very well, currently at the top of the "Sherwood" Third-Order Dynamic Range ranking, where it's been for about 5 years now.
If I'm interpreting your view correctly, then I share it: there is a lot of performance to be had with a well designed analog front end, and the specs of the digital parts can be quite modest and still perform extremely well.
Quite a few radios are direct-- no intermediate frequency, just a set of band selection filters. The direct route does not quite hit the absolute state of the art in dynamic range, but it's close. IC-7300, IC-7610, Elecraft K4, etc. all have this design. I wouldn't be too surprised if one more generation of ADC improvements take it over the line. Certainly there is a lot more engineering might being put into better ADC designs than there is for superhet radios.
Beyond being simpler on the analog side the direct conversion route makes spectrum/waterfall views of the whole band trivial. In theory radios could use this wide bandwidth for improved impulse blanker performance, but I'm not sure which if any do.
Some (like the flex radio, and Elecraft) will do multiple in-one-band simultaneous receive with on each ADC using it... but (other than flex perhaps) the advantages of direct converting a whole band are currently under-utilized. Once they are I doubt there will be much interest in superhet even if the dynamic range isn't quite matched.
I think the future of radio designs though will be finding ways to move the RF portion closer to the antenna(s), away from RF-noisy buildings, and avoiding expensive, lossy, and annoying coax runs.
