That wouldn’t make sense as it would be the user agent (aka your browser) that implements these shared dictionaries and they wouldn’t be able to add non-standard shared dictionaries for libs like react.

If they could do that then they might as well preload the cache with all common libs like react from well known cdn urls.

Committee decided set of dictionaries.

I never cared for react, but I know beyond a doubt that someone influential will ask for a dictionary tuned for it.