I've actually contemplated the idea of doing a node CMS for use on client work. Wordpress lacks nothing, it is just a badly designed architecture with an inconsistent API (for example there are 3 different functions to display a 'loop' of posts, each one has options worded slightly differently with slightly different effects)

Some things that would be good:

1. Contenteditable from the frontend- for when the client just wants to change that one sentence on the third paragraph on the product page or whatever. http://createjs.org/ seems to be a pretty good ready made solution.

2. Repeating layouts- I design and code a repeating element (like photos on the team page or whatever), and the client has an interface to add or remove units, at which point they get updated wherever they are on the site.

3. NoSQL db. SQL is good when one is balancing the books of a large corporation, or doing a survey of the heights and wattages of every streetlight in the country, but it is not a logical solution for displaying documents on the web. It would also be really nice to have a database that could be put in revision control and deployed along with the rest of the site files, as the line between content and templates on CMS sites is a very thin one. https://github.com/felixge/node-dirty is intriguing, but I don't know if there are any unforeseen issues with this.

4. Blogging. Hopefully we could just integrate tightly with Ghost or something like it.

Custom fields similar to Drupal that doesn't rely on a pile of hacks would be a good start.