Few month ago I heard about some initial work on MySQL Proxy software by Jan Kneschke and I thought about implementing some type of MySQL Replication Aggregator based on this software. The idea was to create some piece of software which could get many replication streams, merge them and feed to some mysql slave. This software could be used for backup purposes and many other interesting things. But back then mysqlproxy distribution has been suspended (afaik, by MySQL AB because of some legal issues).
And at last, today MySQL Proxy project has been released to public and it became much more flexible so I think we need to take a look at it and try to implement such replication aggregator patches for it.