I am using the R4i right now, and I like it overall. It is a little noisy, but otherwise it allows me to have a large amount of relatively fast storage within the Mac Pro itself, minimizing clutter outside.
It does fit in nicely with the Mac Pro MPX modules - I just wish it was starting that could be passed along to the new Mac Pro, and sadly it can't because of the MPX design it seems.
I outlined some more modern alternatives to the R4i in this post in another thread.
https://forums.macrumors.com/threads/2023-mac-pro-merged.2391616/page-16?post=32236584#post-32236584
For the folks with a sunk cost in the R4i , I'm sympathetic on why they would want to continue. But the headwinds upon the product are very high at this point. SSD prices in 2023 are just not what they were in 2017.
This new Sonnet product with 8 m.2 SSD slots if you throw 'somewhat dated' , PCI-e v3 4TB drives at it has same raw capacity of the R4i (32TB) at about the exact same price point.
https://www.sonnettech.com/product/m2-8x4-pcie-card/overview.html
(e.g., RAID 1+0 pair two 4's for a '4' and than stripe 4 '4''s for 16TB ). Much less noise . One slot width. One 6-pin AUX cable. Apple is probably a bigger fan of that than of the R4i at this point.
If there are 8 or more E-cores then one E-core could just run the software RAID subsystem all the time with negligible impact on the rest of the system. (probably with enough spare time for other background tasks also).
R4i was likely looked on at Apple as a transitional tool/crutch like Rosetta. Add another 3-4 years and then ask folks would give up on HDDs again ( and see how many more folks they get to take that option).
One big 20TB HDD (with NAND metadata) is still hard to beat , $/TB capacity wise, as an internal Time Machine backup target though.
Western Digital Red Pro 20TB HDD Review: OptiNAND on a Platter
WD’s own approach to high-capacity NAS HDDs
www.tomshardware.com
( Even there though ... NAND consuming some of the data is still coming.)
So J2i is still alive.