I like it! There are two things I would still like though. One would be page rendering in the browser. We often have to iterate several times on a paper adjusting figures, text, padding, etc. to get everything to fit within the page limit. I could write the paper in this and then export it to tex, but that defeats the purpose. The second thing is support of popular LaTeX packages. It looks like I can upload arbitrary tex documents, but that's going to get messy if I have to upload the same packages for every paper I'm writing.
We use github for our papers right now. Less than ideal.
Have you tried our pdf exporter to check page length? We are trying to build it out to where you, as a user, don't have to worry about packages. If there is a journal you would like to submit to and we don't currently have the journal setup as an export template, please contact us and we will be happy to add it.
It's funny how authors worry so much about page length and figure placement, and then the first thing a journal does is remove all of the formatting the author has put in place.