I was just about to mention WebJCS here. I've made 2 levels entirely with the original version of WebJCS, and had no compatibility issues with any 1.23 or 1.24 version of JJ2 or the original JCS. While it doesn't have Plus compatibility other than JCS.ini properties, it does have the unique ability of collaboration with multiple people editing on the fly.

It also looks somewhat like the original JCS if that's of any value.

I'm still hosting a public non-collab version on my server that you can use to load and save files locally, as long as the tileset is present on the server: http://jj2.nl:1998