Far fetched? I hope so
Why? We've had mode-specific radios since. . .forever.
We've had crystal controlled radios since. . .forever.
It may be a specialty market in the end, but we've long had rigs that did less than everything. If someone does this, it would be . . . normal.
The real deal is that the IC 7300 is so cheap (it would have cost about 450 in 1990), that most people can buy it
as their starter rig.
I probably still would find somebody's used rig if I were starting out again today, but I would expect to pay 500, maybe 750 dollars and get something other than an entry radio. And, in so doing, would have paid something similar to what I actually did.
Indeed, the 7300 itself did a number on rig prices, which affects the used market, too.
The real reason we haven't seen digital only radios is that there isn't much money to be saved anymore. The SDR concept is kind of inherently all-mode.
You can get a real good SDR
receiver for about 100 dollars. All mode practically by definition.
Way back when the SDR 1000 came out, you could get a rock-bound, single band rig (again, a receiver) for idiotically small dollars. 40 bucks, as I recall. But, again, all mode.
It's the transmitter that costs.
You can find SDR transmitters or transceivers available via kickstarter. Regularly. They are invariably QRP rigs, but they exist, and are about as complicated as a 2m FM brick. Because SDR takes out all the knobs and adjustment stuff.
Once you get to the end of a SDR QRP
transmit chain, then the issue becomes one of "can I buy the amps that get me from one watt to one hundred to fifteen hundred". You can certainly get from 100 to full legal any number of ways.
And, there are a couple of nice specialty amps that get you from QRP to 100. The KXPA100 will take anything with 5 watts out to that 100. Not as many alternatives here, and the KXPA100 is pricey these days, but all this is pretty much off the shelf.
Moreover, radios like the KX3 or the Yaesu 850D cut the legs out from under most scenarios (SOTA, for instance) that require seriously low weight or portability. Why, exactly, am I bothering with a single mode rig again? Except for the sheer fun of it?
Low cost all mode rigs (and rigs that can be controlled via USB at that) are cutting the legs out from under specialty rigs of all kinds.