The problem is not about the implementation but instead about the back porting of types themselves w.r.t. to ABI stability. Normally back deployed things are available to just be functions. Since this is a full type layout that metadata does not currently have any direct affordances in the language to make it available to anything beyond the newest release.
Personally I agree that the utility for folks to be able to use this before `26 aligned releases of swift is pretty impactful, however there are a lot of moving parts logistically that would need to be solved to back deploy the type itself.
Since it is open source you can copy the implementations as listed; so at least there is a caveat emptor version of a work-around... That is likely workable till I have done some feasibility research on how we could even approach this.