I've found a reference to it in Jean Bacon's Concurrent Systems. She calls it "quorum assembly", but I can't find any other references with that name (slides on cl.cam.ac.uk are by her, or influenced by her work.) I'm afraid it is probably an idea that has been had many times.

The write quorum (number of nodes you must talk to to do a write) must be > n/2. The read quorum plus the write quorum must be > n (otherwise you can read from outside the write quorum).

So the n=3 case is simple, RQ=WQ=2 as you suggested. I think it wasn't very successful in larger cases because n/2 isn't much better than n, and you have to do some kind of synchronisation between the nodes which is tricky to get write (consider how the write nodes know the other write nodes have done the write.)

In practice, hierarchical schemes where you are reading from a slave which might be behind the master are more common. There you can have 1 write node and n read nodes. Since reads are generally more common than writes, this is great.