I personally like the idea of limiting CakePHP to backend stuff.

The list you mention is not particular for sproutcore, those are just the technologies most people tend to work with when building web sites/applications. And I don’t see anything wrong with that anyway

Sometimes you have to take baby steps to embrace a new application architecture. All those things you are talking about beyond the client-side Javascript are really new. For most developers, simply understanding how to use CouchDB is a tough task. The mere fact you mention it places you in the minority that understand.

Be brave! Try something out even if it’s something really simple. I sort of understand what CouchDB is doing because of my work with eXist, and how new paradigms cause people to retreat to old and familiar things.

But, there is a growing trend the other direction and it’s centered around javascript. It is feasible (though I don’t know if it’s been done) to build an entire data-driven application in just javascript (plus HTML/CSS):

Javascript client side like we all know and love
Javascript server side through the relatively new Aptana Jaxer server
Javascript/JSON as a query language to the database with CouchDB

In this scenario – you would never need a middleware language like PHP because javascript can do client and server side processing. Also, SQL is a non-factor because CouchDB uses JSON objects for querying the database.

But like I’ve said – I haven’t been brave enough or had time enough to actually give this stack a try.