Like I said earlier, it wouldn't surprise me to see a new arch show up for the rest of the X-line within a year or two. But who knows. I've been wrong before, yhey might have decided that they want to thin out the linup also.
I could see a split like this being a thing, otherwise:
x1000 old arch, no probe compensation
x2000 new arch, +DSO, still no probe comp
x3000 new arch, +probe comp, +50 Ohm.
x4000 new arch, +bigger screen + really deep mem, +additional arb port.
x6000 new arch, up to 8 channels.
I assume by "probe comp" you're really meaning AutoProbe (at least the more limited version the 3/4/6 series has).
The list you have does roughly make sense, I'd probably say new 4k probably keeps at least a small bandwidth bump over 3k.
It's the 6k I'm not sure about, it's a wonderful scope (I love mine), but it's very close in many ways to the S-series, so it would need something special to keep it post-refresh, especially if the 4k was also being kept. One possibility might be to somehow allow the scope to be hooked up to a Windows PC via thunderbolt (external PCIe) to turn it into a full Windows-running scope when needed.
I'd also guess that we'd see the models released in the same order as they were for the current run, so a 2k & 3k first, then about a year later a 4k, and another year or two for the 6k, and as old as these models are, other than perhaps competing with the (lower end of the) new Tek 5k series at the high end, and some of the R&S units, I don't think the pressure is there to move as fast as they could.
Remember there's been no firmware update since late 2017 for most of these models.