I don't think CouchApp is a good choice for any target market. Most people eventually need to execute more arbitrary code on the serverside. Theoretically the Wordpress crowd would be a good target, but they don't like to code. You would need to aim for zero configuration. (it's fine, just know your market)
Personally, I wouldn't feel safe to rely on CouchApp. What if my site goes viral and I need much more functionality? I'd have nothing to build up on, and I'd eventually need to rebuild on nodejs or something else.
A Couchapp has features that are trivial in couchdb (replication, map-reduce) but require more setup in traditional server side code. The target market will be applications that value these tradeoffs.
If you decide you need something else, I don't see the problem with having some parts of the application served by couchdb and some served by node. Put it behind varnish, cdn the static content, add a queueing system or whatever...
I think a couchapp is a decent way to prototype something out and if it goes viral you're going to be rewriting everything anyway no matter what system you use.