It's immaturity, probably driven by a lack of development focus/effort/priority.
Plenty of other mainstream vendors supported these concepts on older platforms that reached EoL before the 6610 did.
/126 is pretty standard for P2P links when you don't want to burn /64s (and avoid neighbor cache exhaustion attacks) and the platform doesn't support RFC6164 (which dates from 2011).
The ICX 6xxx switches are well featured for the price but things like this are downsides.
RFC6164 was added in the icx7xxx series so indeed the 6 series doesn't support /127 links. I've used /126 links quite a bit now on the 6 series platforms however with zero issue, however they are all indeed using the second address, not the first. Are you the guy I discussed this with on reddit?
Sure, they have some special no touch zones, but I think saying "if you want to use IPv6, you HAVE to use a 7 series" is a really vague overstatement - I'm using 6 series in production in a few places for a few years with zero issue - no issue with ND expiry either, at least on xen hosts, live migrates between physical hosts, I certainly don't see any IPv6 downtime, or if there is it's far too small to be measured. Taking IPv6 tables in via BGP in a couple locations as well and performing a good amount of filtering, no issue. They certainly have some blind spots, but if your use case doesn't involve them (which is a LOT of use cases), they work perfectly fine for v6
Also, if any of you are paying Ruckus customers with a 6 series under support, your SE will gladly take these bug reports and forward them to the engineering team for fixing, I know last year at least 1 resolved issue in the release notes was something we reported beforehand