I don't think they have much of a choice about keeping off-element cards from those decks. Remember: water did not win last round so they get 0 transmutes. They are likely to be forced to convert 24 off-element cards just to get enough in-element quanta, not to mention other in-element cards. Still, with what they beat round 3, Dim splash is likely, especially against us. Both PDials and UGDials could seriously wreck most of their options (except sanct stall, which is likely to be too fat and full of quanta to revive, despite them keeping 13 cards from that deck).
Actually, UGDials beats even Sanct stall if you blow up all UGs at once :p