Yeah there's about zero chance of Zen 2+. I'd actually be a little curious if there would be any point at all to keep producing Zen 2 chiplets, or if they could just put Zen 3 chiplet paired with the Zen 2 IOD. Perhaps the performance improvement would be enough that the 3950X might move to being 12 core, and the 8 core chips being 6 cores. Maybe they'd lose a bit of multi-threaded performance but it'd be made up for by the extra IPC (so they lose say 20% from 25% fewer cores, but with the 15% IPC its really only losing 5% in highly multi-threaded, while it'd maybe gain in lower threaded and other tasks like maybe gaming; or maybe ones where the full cache isn't working or something). But this way, they make use of the defective Zen 3 chips, while keeping the fully enabled ones as a premium. And it'd let them clear out IOD if they need to do that.
We'll see about Zen 3+, I think it makes some sense as I have a hunch that Zen 4 won't be til 2022, so that'd leave 2021 without new product. Which going chiplets means AMD can update just part of the overall CPU package. Seems that the rumor about Zen 3+ is it'll bring probably a new I/O that could offer DDR5 support. Which it might could also be that the big thing is APUs go chiplet, which would let them keep the AM4 socket and boards (whereas going DDR5 and/or PCIe 5 will likely require some updates to the boards).