tko

It's not dead, it still receives updates (as recent as 4 days ago). There's an overhaul in progress called TKO (https://github.com/knockout/tko) that is supposed to bring Knockout up to date with ES6, a better plugin API, and other nice stuff.

The devs seem to be mainly working on an updated version without a lot of the legacy code: https://github.com/knockout/tko

I mostly agree with this - bite-sized chunks is really the main ingredient to success with complex code base reformations. FWIW, if you want to have a look at a reasonably complex code base being broken up into maintainable modules of modernized code, I rewrote Knockout.js with a view to creating version 4.0 with modern tooling. It is now in alpha, maintained as a monorepo of ES6 packages at https://github.com/knockout/tko You can see the rough transition strategy here: https://github.com/knockout/tko/issues/1 In retrospect it would've been much faster to just rewrite Knockout from scratch. That said, we've kept almost all the unit tests, so there's a reasonable expectation of backwards compatibility with KO 3.x.

I designed tko (https://github.com/knockout/tko) to make it easy to re-use the best parts of Knockout using tree-shaking ES6 imports. When experimenting with substituting a few modules, I've gotten it down to 4.5k gzipped. It's still quite early on (alpha), but already some folks are using it in production. Plus, it's mostly backwards-compatible with Knockout. While it might not be an ideal, usable solution for this problem yet, it's definitely moving in the direction of filling exactly this niche (among others).