Officially, no.  And unofficially, yes.  Here's the logic.  For certain public API methods to have meaningful return values (i.e., to stick to the interface contracts), if you are using DIST, synchronized communications are necessary.  For example, you have 3 caches in a cluster, A, B and C.  Key K maps to A and B.  On C, you perform an operation that requires a return value e.g., Cache.remove(K).  For this to work, the call needs to be forwarded to A and B synchronously , and would have to wait for the result from either A or B to return to the caller.  If communications were asynchronous, the return values cannot be guaranteed to be useful - even though the operation would behave as expected.

Now unofficially, we will add a configuration option to allow you to set your cache mode to DIST and use asynchronous communications, but this would be an additional configuration option (perhaps something like break_api_contracts) so that users are aware of what they are getting into.