Protege detects if the file you have loaded changes and asks if you want to reload.
Very useful for working in dual tool mode, but only works in one direction.
OE should also detect if the source file changes and a dialog should ask the user if they want to reload. That way edits in P4 can be seen automatically in OE (now we have obo2owl2obo)
Also useful for running reasoners externally
This may not be completely trivial because of the unusual was OE handles files (e.g. no "save", only "save as")
Not required for 2.1 release but high priority feature for 2.2