Would it be possible to add a format legality on the deck-builder?
If so, Oathbreaker is a great format started by a charity organization called Wierdcards. It is a format similar to Commander however instead of a legendary creature as your commander you have a planeswalker. You also have a 'signature spell' which is an instant or sorcery within your commanders color identity that can be cast when your commander is on the battlefield (Commander Tax still applies to both). It is a 60 card(58 + commander + signature spell), singleton, 30 life format with a ban list similar to that of EDH with a couple of additions (such as
sol ring,
mana crypt and
primal surge).
I think it would expand the format despite it not being recognized by WOTC and would be a strong addition to the site.