Variables that can be used across multiple automation runs would indeed be very useful. Especially for blueprint creators.
Bonus points if they could restore their state after a HA restart.
I had a talk with Frenck about that once - he mentioned it could lead to race conditions - especially with lists. And that there was a PR once that would introduce a key-value-store that could tackle the same problem. https://github.com/frenck/spook/pull/509
IMHO it’s not as practical though since the automation would need to scope the key somehow and would have to do some kind of cleanup when deleted. But maybe I didn’t get the idea 100% right.