Honestly, fixing the issues with EoC, and providing things like revolution is where they should focus their effort. I don't think Legacy mode will work out how they think it will.
Resolving the keybind issues, and fixing all the little places where enter-to-chat is not consistent. Stop randomly hiding action bar so that it doesn't let you do enter to chat.
Resolve the issues with keybinds not being fluid, and not responding quickly.
Resolve the issue that NIS canot be made to look like the old layout. Add abilities to move windows around in such a way that this works.
Pull out the windows that have sub-windows nad make them act like normal tabs, instead of tab within tab. Let us keybind those how we want.
Allow the old option-stones to be enabled.
Essentially, let players configure the current system to work the way they want. Don't just hack the legacy interface back in.