Comment Re:Interface to online compilers (Score 2) 70
At writeLaTeX.com, we compile automatically, typically every 5s-10s. One of the things that makes it work is that the server can cache most of the stuff that doesn't change often, such as the figures. This does require a bit more sophistication on the client end than just uploading all the inputs for every compile, but it's definitely possible.
In terms of packages, we run a full TeXLive distribution on the back end, which covers most things. (But we still have to install CTAN packages on request from time to time.)