Comment by pas

hmmm... could this be solved by "vector clocks"? if producers are emitting something that depends on a previous event they send the id of the previous event. (so like capabilities, you need proof of "data access".)

or the problem is that again this is O(n^2)? (because then the consumers now need to buffer [potentially] n key streams (and then search for them every time - so "n" times)?