I spent all day looking for a deck editor which included a feature like this, but was unable to find one. I play almost exclusively in EDH, as well, and having the ability to create custom subsets or groups of cards within my decklist (for example, "removal," "lifegain," "hugs," "rattlesnakes," etc.) would really help facilitate tighter deck construction.
An alternative would be to add an option for an editable "notes" or "tags" column to be displayed in the deck editor, along with name, type, cmc, etc. This way, I could type my own tags into the field for each card, and use the editor to sort the cards in my deck by that field (the same way one would sort by name, cmc, etc.) This effectively accomplishes the same task: when the cards are sorted alphabetically according to tag, all of the "removal" is put together with itself, and so on with "hugs," "scary clowns," or any other tag I decide to add to a card.
In fact, this alternative would probably be much easier to add on the back-end, and much easier to use on the front-end. It doesn't require developing any kind of interface or hierarchy system for custom sorting, nor the creation of unique fields, nor does it force players who don't wish to sort their cards like this to contend with needless features; instead, it is available to those who want the option, and completely out of the way for those who do not.
I'm really hoping to see a feature like this implemented in future updates.