The 20K deck slots are easy. I have 3.8MM runes kicking around, with no way to spend them (I own every PW that has been made available for crystals, with two or three deck slots each). I would advocate, instead, for a show/hide flag on theme decks. They would remain visible in the Planeswalker screen, but be (potentially) hidden at the event level. I also have a database that I use to track all decks, so I can recreate any on the fly, which makes it a little easier for me to walk away from one.