Thanks for referencing the post here.
I've got a handful of sets. If you have Systainer3, and interested in trying them out and sharing the feedback with the community, please get in touch.
I'm excited for this rail kit to finally be here. I don't have 'stock' per se yet, so I'm not offering for sale yet. Why am I excited? I feel like this really completes one of the promised features of the Systainer3. The builtin/molded in rail of the Systainer3 wasn't really possible until these kits came around for the average user.