Also, it would be pretty idiotic to put 10GSa/s or 20GSa/s hybrids in entry-level scopes with bandwidths of 1GHz and less where such excessive sample rates have zero benefit.
Not in year 2018+. Isn't it idiotic to put 5GSa/s ADC into 100MHz DSOX3014T?
Not when the scope series offers bandwidths up to 1GHz, which the DSOX3000 Series does. Also, the DSOX3000T is pretty much a DSOX4000A in a smaller case and with smaller screen, and that one goes to 1.5GHz, hence the 5GSa/s sample rate. Using the same front end and acquisition system on the DSOX3kT reduces costs and gives the DSOX3kT additional features over the DSOX3kA.
There is absolutely no point putting a 10GSa/s+ hybrid in a scope that has a max BW of 1GHz (or even 1.5GHz for that matter). All it does is using up available sample memory faster, without providing even the slightest benefit to the user.
I doubt any sane engineer would do that.
Also, ADC is just a CMOS chip (okay, two chips MCM for 10-bit DSOS ADC). The more of them you make, the less each one costs.
Not as much as you think. Plus the costs only go down after you've produced a large number, which means there'd be a pretty high initial outlay that KS would have to carry.
I think in several years DSOX3000/DSOX4000 replacement should be up to 2,5GHz or even up to 5GHz BW. MSOY3254A.
Again, that's extremely unlikely. The bandwidths haven't really changed in the last 20+ years, 100Mhz was entry-level back then as it was today, and 500/600MHz is still pretty much the general limit of the entry-level segment, and 1GHz/1.5Ghz the upper limit of the mid-range segment. And that is for a reason, because the general bandwidth requirements for entry-level and mid-range classes haven't changed dramatically over the years (high-end on the other side has, quite dramatically so), and there is no sign that this will be different in the next 10 years or so.
The successor of the DSOX3kT will most certainly still cover BWs up to 1GHz, and it's successor will also still cover BWs up to 1GHz, and so on.
I'm sorry but none of your ideas have any roots in reality.