If you want to de-duplicate data, you need to have a sufficiently large data window to find such data in the first place. There isn't much time to transfer data and operate on it when your target is sub-100ns added latency, so the data window will be quite narrow and de-duplication opportunities quite few by necessity.
With encryption on top, it probably lands in "forget it" territory unless you add an extra storage/cache tier between DRAM and whatever media the swap file resides on.
You're right on de-dup, that would only work at storage level and with memory encryption that's far too late. That comes from me working too much with RHEL VDO, where (storage) compression and de-duplication are merged into one process.
As to memory compression and encryption: memory encryption is being done today even on x86 and the impact seems quite low enough, people might not even notice. I can barely tell with my 5800U based notebook or my 5800X based workstation, which both support full memory encryption on the BIOS.
Currently on the client side the granularity is only at the physical host level, even if the hardware is all the same as the servers, where it's supported at the VM level with EPYC (Intel is just as bad and won't support per-VM encryption on VMs on Tiger Lake).
Including this Swedish IP block would have to be done before the encryption, but I don't see why it couldn't be done.
As for memory compression I mostly keep wondering why it's disappeared in the mean-time, because I believe it's been around for a long time and IBM even sold a Xeon chipset long ago (MXT?) that supported it. But that was at a time when memory controllers wheren't yet included in the CPUs.
I found this old hot-chip paper on the topic:
https://old.hotchips.org/wp-content/uploads/hc_archives/hc12/hc12pres_pdf/IBM-MXTpt1.PDF
Memory
compression encryption must be a long time mainframe feature, because these used to be clouds before the word cloud computing was invented to describe what they had done for decades.
I don't see a lot of swapping these days on 2TB machines... but I remember my PDP-11 (DEC Professional 350) doing a lot of swapping--even with some benefit... at 32Kwords maximum segment size.
Ah and I believe one of my first mobile smartphones, the Samsung Galaxy i-9000 actually started swap to zRAM with one custom ROM to eke a bit more life out of 512MB of RAM.