You're right, I can't speak to multiple riders (no pun intended). Obviously, if group rides is a major reason for having any comms system, and the 20S can't do it, then it's not a good choice. I don't (verges on "won't) do group rides, so it's a non-issue for me. It works well when I do ride with a friend who still has an SMH-10. I've got more features than he does but the job, comms, works as expected. Maybe the 20S EVO or 30K does group comms better?
I don't have an iPhone, so Siri is a non-issue for me. Using Maps and Google Assistant at the same time is essentially a train wreck. Sometimes one app answers, sometimes the other, but's that's a Google/Android issue. The 20S doesn't get in the way.
I don't recall if Ryan F9 says it explicitly, but it does appear that Sena is slipping behind on the basic job, and spending more time on helmets and supporting different helmet types. As I've said, ironically customer-Sena comms appear to be almost non-existent. Otherwise listening to customers might move development in a more competitive direction.
All of that said, I still like the 20S, and Cardo still fails on sidetone (yes, it matters that much to me). For someone who rides alone or with, at most, a couple of riders, I'll still recommend the 20S. But recommend looking for a deal on eBay, etc.
I'm puzzled by the "don't like it, don't want it" response to sidetone. I found some research into sidetone use with telephones (smart, wireless, or wired). By a large majority, users found that not having sidetone was very undesirable. As someone here said, it leads to "can you hear me now", and speaking louder than is warranted. The phones seemed to be "dead". I found that to be the same case with the SMH-10. The feedback from sidetone matters.
Side comment about mounts. The SMH-10 mount uses a tab, long enough to be springy, to hold the unit in place. Looking at the Cardo mount Ryan F9 showed, I'd be equally nervous about "one wrong push and bye-bye". I tried making a "leash" for it, but couldn't make it work. The problem was attaching a thin stainless steel fishing leader to the back of the SMH-10. A thin guitar pick with a hole in it fit in the available space. Finding an effective adhesive was the problem - nothing I tried made a good bond. I wonder if anyone tried the same thing with a Cardo device? I get that the Bold voice commands make button-pushing irrelevant.
ADDED: Since the Bold functions by voice, there's little chance of a button push releasing the catch by mistake.
I emailed Cardo about sidetone - I'll report whatever comes back from them.