I recommend asking the Airtable developers directly. They typically don’t share their development plans openly.
While it may be a “basic feature” of React, the subset of React features that are available via the blocks SDK are intentionally limited by Airtable, mainly because apps made with the blocks SDK can’t run just anywhere. They need to be compatible specifically with Airtable, and there’s a very precise way that has to happen, and very precise reasons (security being just one of them) driving those decisions. Only the devs can say for sure (if they choose to do so) why environment files aren’t allowed, and whether or not they’ll ever be allowed/supported.