WordPress isn't going anywhere any time soon. There is too much momentum behind it.

As you point out there have always been competitors who try to make things simpler. Some of them have done alright, but none have slowed down the growth of WordPress significantly.

I think John will do a great job with Ghost and it will probably do better than many of the other competitors. He's a clever guy and the project has the support of many fine people. But I still think it's impact on WordPress will be minimal (well apart from pushing us make things more simple).

Ghost will probably find a niche between WordPress and Tumblr somewhere. It makes for interesting watching.