Mode editor upload to server

I want to use the mode creator to create my own mode but there seems to be no way to make changes in the mode creator persistent aside from copy'n'pasting from the mode creator into another editor, which is silly.
So I added PUT support to static.py and corresponding buttons and Ctrl-S bindings to the 2 panels of the mode creator.
With these changes in place one can start static.py with e.g.

./static.py --puttable=lib/ace/mode/newmode_highlight_rules.js,demo/kitchen-sink/docs/newmode.rudl

and then work in the mode editor with Ctrl-S/Upload-Button saving directly to disk.
Allowing write access to any file under rootdir is too dangerous in an unauthenticated setting. While changing the default listening interface to 127.0.0.1 does mitigate the risk somewhat, there's still a risk in shared computer settings (e.g. a university computer lab) where other people might ssh into the computer you're using. In addition to this I like to protect myself against my own mistakes. I may want to switch to a different highlighter while editing my mode for comparison and wouldn't want to accidentally save changes.

What is the maximum line length you tolerate?