Any comments on the map_with() I added to be preferred over flat_map() because it more consistently fits into the naming scheme with transform_with() and recover_with() ?
How about the depend() functionality; does it fulfil all expectations?
Anything else missing in Concurrent/Promises/Futures?
If not, we might push it over to 8.0 together with the testsuite, since it does fix a few serious flaws in the current 8.0 implementation (the new fixes eliminate a few deadlock cases).