No VPN? SSH as a plugin ???
Using a Chrome plugin for SSH is taking unnecessary risks. I see no reason why there couldn't be a terminal application on the Chromebook.
If it's due to UI, maybe there could be a way out of the GUI - IIRC the Chromebook runs on X-Windows.
If you can't hack it in a way where ctrl-alt-f1 will get you to a genuine linux getty, running standard GNU/Linux command line software after a recompile, I don't want a Chromebook for development.
Unless you have money constraints, it makes more sense to purchase a real laptop - a macbook if you need the battery time.