I really don't think we have anything to worry about. SOMETHING is going to pop up which tackles WordPress head on. WordPress has too many deep issues which can't be easily solved in a backwards compatible way. Once someone creates something to compete and gets even a little traction, I assume it will rapidly gain in popularity and eventually take a huge chunk of WordPress's marketshare.

Until that day happens, WordPress will keep chipping away at more and more marketshare, but each little chip just adds more encouragement to those who are building the competitors.

I don't think those of us deeply ingrained in the WordPress community should fear this though. The internet is a big sea, and there's room for more than one big fish in it ;)