Last I looked, writes on optane devices didn't go through any caches and went straight to V-NAND, obviating the need for PLP. On top of that, optane is byte-addressable for reads and writes (i.e. not block-based) and thus doesn't need to go through the read-erase-modify-write fandango that NAND has to before a write can be committed. It's this property that results in its incredibly low latency.
If intel say the drives don't feature Enhanced Power Loss Protection - basically a trade name for a bunch of capacitors as far as I'm aware - it's because optane's don't have them and don't need them.
Then for my case, I will probably use the 900p for SLOG.... Not to run this topic off-track. I do still think that P3600 will suffice as a very good SLOG. Especially considering that the backend devices are HDDs and not SSDs