As unique units, with their own bespoke Kroot rules?
No, at least not at the moment. I think there was some vague wording suggesting
FW might include 8e rules for the out-of-production Kroot units, but nothing concrete from my memory.
However, those models need not go to waste. Kroot are, above almost all else, adaptive little space chickens (not Tyranid level by any means, but very adaptive), and
GW has recently introduced over a century of progression time in which you can explain your Knarloc Riders (and the Kroot accompanying them) as evolved Mercenary forces independent of the T'au Empire (they've been doing that even in the previous fluff) while using the rules of another faction.
The most obvious factions to replicate would be Aeldari (generally lightly armored, generally fast/quick) and Orks (numerous, ferocious in melee, generally lightly armored), though once you add in enough Mekboy-eating Kroot or secret T'au Empire support/research, you can start branching off into the more heavily armored factions (Space Wolves and Blood Angels in particular seem suited for Kroot equivalents). That's where I plan to use my own Knarloc Riders - as Thunderwolf equivalents (converting armored kroot is kind of a pain, and/or expensive, so its been a long-ongoing project).
Honestly, aside from Necrons, there's really nothing a Kroot combined with Ork-Kroot Hybrid or T'au Technology couldn't replicate in terms of rough equivalency in rules/effectiveness. There's even room for titans - I'm slowly and without skill scratchbuilding a Warhound using Devilfish/Skyray parts, some plasticard, and a few odds and ends.
For Necrons, you have renegade T'au AI Drones that managed to approach a Singularity in technological achievement, and being AI in a grimdark Sci-Fi setting, are creating a new AI empire of the GREATEST Good.