For us, separating streams has been VERY handy in the past, when the ES was corrupted. Instead of the whole ES dying, only that stream died. Since it was physically separated by file/db, it could be rebuilt without side affects to other ES’s.
Maybe GetEventStore will never corrupt, but if it does, I fear the whole system throwing poison, instead of just one stream.
Storing into separated physical backing stores would help me sleep at night.