Having a tab-based DM Editor is something I'm sure has come up in the past, but it was brushed aside back then because frankly the focus on other things was much higher.
I think, now, is a good time to bring it up again. I think all BYOND developers would benefit from a tab-based DM Editor wherein once you opened a file a tab for it would open up in a little tab bar up top( et al Notepad++ ) for that file. In addition, once you drag this tab away from the tab bar a window instead is formed wherein you can edit the file alongside whatever other tasks you might be doing.
This would be a great addition for multitaskers and people who want to get things done at a higher speed.