If we have several process instances from different process definitions, all of them waiting the same signal and only one of these process instances throws a RuntimeException all others not related will not move forward as well, because they are executed sequentially in the same single thread.

That creates a strong dependency between the process which are not in fact related.

Async signals can solve that, however they can potencially impact on performance given that each process will continue in a separated transaction.
To solve this trade-off such behaviour should be configurable by users.