But the target is not moving that fast. The "core development team" has very much resistance against protocol and block chain rule changes. So if someone finally succeeded in turning one of the alternative clients into a fully functional node, it wouldn't be that hard to keep up with changes in the Satoshi client from there on.

Also, Gavin was talking in another thread about introducing some kind of PEP process for the Bitcoin protocol(s). This would make it less hassle to keep up.