Until there is serious competition and demand, I think the R75 will soldier on forever, especially since Yaesu and Kenwood long ago abandoned the market leaving the whole pie to Icom. My hope is that Icom realizes how many they have sold over the years, and will stock enough replacement parts for repairs when the analog devices become unobtainable through normal means.
About the only competition *currently in production* of similar capabilities is the Alinco DX-RX8(T). I have both and while the Icom is a better receiver specification wise, to find those differences depends on how serious one gets. This is especially true when one considers that to take an R75 to the next level with multiple 9mhz and 455khz filters, they will cost nearly as much as the R75 itself - and provided you can actually justify them, and in some cases actually obtain them as some of the desirable oem units are either not in production, or one knows how to get them from Inrad or other sources, AND configure the R75 to use / stack them properly.
The R20 will do likewise for the same reasons as a niche product for a niche market. Formerly, "DC-to-daylight" spectrum coverage was a cool selling point, but these days most people are advised to get a scanner if you want a scanner, and get a tabletop hf receiver (like the R75) if you want one. Otherwise, there is a small market for those who enjoy shoe-horning the R20 into doing both duties. It makes a fine conventional *receiver that scans*, but for some the programming is cumbersome unless you live with it daily. Shortwave reception if using anything other than memories is a huge drag twiddling the ratcheted vfo knob - and prone to wearing out if you scan the bands. I think the biggest competition here is the AOR handhelds. Both are really marketed to people that already know what they are doing, and are willing to live with the compromises of a dc-to-daylight package where efficient antennas are usually attenuated!
I'm not sure that Icom will ever produce any trunking / digital upgrade to the R20. One issue might be the mere cost of licensing the codecs for a niche product in the first place. And the cost of these high-quality Japanese units may never be able to compete price-wise with lesser-quality scanners manufactured elsewhere. Unfortunately, most consumers only look at price, and don't concern themselves with long-term quality.
One thing Icom could easily do is fix the mis-step they took with the RX7, which had more modern memory management and other features, and put it into the R20 chassis, solving the poor audio situation, and toss the "cute" features like ambulance/skier/race car/airplane icons. Reduce the price by tossing the HF section (leave that up to the R75). That to me would be a worthy upgrade to the R20, even if still only conventional vhf/uhf coverage.