I have seen several emails/blogs about mongodb and 10gen musing over FTS. There are a few projects if i am not mistaken that have "bolted on" FTS to mongo but I do not think they have had the same development/LOE as riak search. But with out playing/testing with all those options I can not speak authoritatively on the topic. FTS no doubt will be an emerging factor in the future in the NOSQL landscape IMHO.
Check out riak, they are continuing to develop their full text search engine that integrates with their data store. I have yet to play with it but it looks rather promising and you wont have to deal with trying to bolt on your lucene/solr into couch/mongo.
I am with thaumaturgy, i hope this fails its just another application of old school thinking. The same thought processes that brought us these horribly designed protocols and their bandaid fixes (dns sec anyone?). Hopefully these old guys will just retire and leave ietf and other such organization that they seem to monopolize to the generation they created this mess for.