There's an FPGA in all of them, but the Zynq has a dual core ARM with two vector NEON FPUs. From what I've seen the Zynq based scopes are all using 7010 devices, so at the price of some fiddly soldering, one could upgrade to a 7020 if one ran out of FGPA gates. The Rigol DS1000E and DS1000Z series do not use Zynqs. Most likely because of when they were designed.
I bought a Zybo Z7-20 and a BeagleBoard X-15 for dev work. The documentation for the Zybo is pretty mediocre, so I got a MicroZed to use while I work through all the tutorial examples for it. I've got an Instek GDS-2027E which I shall use for testing once I get that far. This will take a while as I am prone to playing with other shiny baubles that catch my eye.
I'm an old hand at DSP having worked in reflection seismology my whole career. I can think of a lot of tricks to teach a computer that can sample at 1-2 GS/S and implement real-time FIR and IIR filters and FFTs. I haven't quite reached the $1k mark for the project , but as the saying goes, "The chicken has an interest in breakfast, but the pig is committed."
I'm chaffing a bit at the moment because @cellularmitosis sucked me into volt-nut land. I'm working on a small Peltier chamber today built around an old CPU heatsink and fan, a couple of TEC1-12706s and a 4" surface mount steel electrical box. This is an experimental build before I build a larger unit. Mostly motivated by I bought 10 but needed 8 for the big unit plus 4 high temperature units. So a more limited range box seemed a good use for the two extra devices.