I have no idea what will happen if conducting this experiment it may end in random noise.
just that no one has posted a circuit like this anywhere. maybe because it doesn't work.

To what end? Do you want to "mix" (in the audio sense) the signals?
Logic gates are nonlinear in that sense. An adding circuit (audio mixer) is required.
yes I know the audio at some point in the signal path needs to be recovered as analog from the digital output.
in analog audio mixing the results are well known and well documented we all know that.
Check electronic music sites, and work of Moog, etc. on polyphonic syntheses.

I know about Moog ARP and Japanese Roland history, the many good analog synthesizer sites
why try this or experiment
there are some things one can do with a digital output that one can not do with a analog output
example clocking sequencers and digital circuit bending.
I started with the popular
Atari Punk Console and decided add to both ends of the circuit with a big bag of 555's from AliEx.
the front end is the circuit posted here. middle is the un-known digital circuit

and the rear end does work as a digital to analog converter.
I am posting to see if anyone has tried this before
thinking about this it looks like a high frequency clock is needed to coordinate the
digital mixing at both the top and bottom of the frequency's to be combined. this is getting complicated
if all else fails I can copy
the Atari Punk Console circuit 12 times in parallel, then tune it to scale. that's 24 knobs to play with.
add two sequencers on analog audio mixing output, 18 more knobs to play with. mission accomplished