Zen3+ will be on AM4 with official support on x570/x570S and likely B550 chipsets. I wouldn't expect it, but extended support for x470 and B450 by AIB's isn't entirely improbable as well. Beyond that point I'd be skeptical of it being supported short of bios mods similar to Z170 and coffee lake.
It would make no practical sense for AM4 to force a new chipset for Zen 3+ on a new socket then switch the socket support to DDR5 and/or another new chipset shortly after for Zen4. That's just added expensive and with supply logistics right now with chip shortages would be asinine as well.
Risking losing a CPU sale to Intel for a newer socket and low margin chipset that's still based around DDR4 isn't worth it unless Zen3+ also bumps up memory channel support beyond dual channel. If they went with triple/quad channel DDR4 it's a long shot far fetched possibility, but with chip shortages I doubt very much for that to be the case. Let's just consider x570/x570S/B550 chipset all, but confirmed for Zen3+ because odds it isn't are in the order of 10 to 1 or greater. I'd absolutely like to be wrong on this though. I really wouldn't mind at all.
No worries tomorrow we'll see a leaked rumor by AdoredTV re-hashing more or less exactly what I said above with rumor mill in full hype mode. There are only so many viable options can take with this and a Zen 3+ on a new chipset and socket for DDR4 that just dual channel and PCIE 4.0 would be viewed horribly and be a bad chess move at the same time especially with chip shortages. Some people literally wouldn't be able to afford that transition and AMD could lose a sale to Intel as a direct result of trying to force their hand on MB transition.
Liquid immersive cooling of entire builds (mobo+CPU+RAM+etc.) is a thing, just so you know.
Submerged mineral oil builds are among the most fascinating think outside the box cooling builds to consider. As a enthusiast the different angles you can take with one are a fun consideration. The ways to go about and why you might do one methodology over another is fun to contemplate. In fact you could combine liquid cooling with radiator with it. You might submerge a SFF case that can mount a radiator on the top right into a fish tank. In turn that would allow you to pump heat thru the radiator to dissapate into the air so the mineral oil ambient temperature doesn't rise as much.
