Future Developments: Using Nutch 2.0 to crawl websites and send to DB such as MySQL

I don't really understand the question here, but maybe I'll answer it anyway.

As far as I'm aware of, there are currently no efforts in integrating any of the three systems with the Search API. I also haven't yet worked with any of them, so am also not available for working on this myself (even if I had the time). In my opinion, it's a great suggestion though. Maybe you should create issues in their issue queues and ask them if they'd be interested to build their modules' next versions on the Search API.
There'd surely be various advantages in it for them, too, and I think a number of people will testify that I'm very dedicated in helping people to develop for/with the Search API. ;) Also, additional documentation for developers is on the way, and the module is about to finally get to a stable version. So I think right now would be a really good time to make the switch, if they'd be at all interested.

The CouchDB module looks like a dead project.
ElasticSearch is coming courtesy of JoeMcGuire and he's already said he intends for it to work with Search API.

Include them, no, definitely not. But it is already possible and very encouraged to add support for them in additional contrib modules, like search_api_solr does for Solr.
As I said, I'm in no position to do this myself, but as Shadlington explained, integration with ElasticSearch is at least planned. It's, in any case, not in my hands, and also doesn't really depend on this module. This module is already capable of supporting those search systems (as far as I'm aware of).