It's now clear that Optane SSDs are 100% compatible with older chipsets and CPUs - guesses about CPU instruction sets are mistaken.
Over a year ago, ServeTheHome.com tested running their entire website on Optane 900p SSDs, to see what difference it made. They reported that
We put copies of the entire STH main site on a dual Intel Xeon E5-2698 V4 system that is identical to another system we have set up in the hosting cluster save that this node had 2x Intel Optane 900p 280GB AICs, 2x Intel DC P3600 1.6TB NVMe AICs, and 2x Intel DC P3700 400GB 2.5″ SSDs.....
We [did] a second day entirely on the Intel Optane 900p 280GB SSDs [and tweeted] "The STH main site is being served via ZFS mirrored Intel Optane 900p NVMe SSDs for a few hours today just to generate some test data.."
— STH (@ServeTheHome) January 2, 2018
What's interesting in this post is a throwaway comment - the "v4" bit. The Xeon E5-2698 v4 is a Broadwell EP CPU (LGA 2011v3). From that alone, it's clear immediately that S.T.H. found Optane SSDs to be compatible enough, and stable enough, with Broadwell era CPUs, to serve their entire site during testing, and to gain very positive impressions on the combination as well.
People have even reported getting Optane to work on old Ivy Bridge 4790k motherboards running Windows 7 - suboptimally for sure, but clearly no fundamental hardware incompatibility.
tl;dr answer:
The limits on using Optane SSD like you'd use any other SSD, are apparently just the need for NVMe support (in the chipset+BIOS/UEFI+driver) and the lack of appropriate physical connectors, both of which are more likely to be missing as boards get older.
Very old versions of NVMe in the BIOS/UEFI might also need to be updated - there are hints about this in a couple of forum posts but no confirmation one way or the other so far.
- (Relevant and not-well-known resource: bios-mods.com is a website that specialises in updating bios firmware modules for NICs, SATA, RST, USB, etc to newer versions, so the boards can be used with newer hardware, drivers or OSes, it could be helpful if stuck)
The main reported issue in older chipsets/CPUs seems to be related to NVMe driver support (in Windows at least), which wasn't yet included in Intel RST at that time.
The requirement for a "latest CPU+chipset" only seems to apply if you want to use Intel's Optane-specific caching/acceleration/NVDIMM functionality, because that needs chipset support. But ordinary SSD use - apparently no issues.