I'd like to see some of them play more non-core races in Campaign 3, whenever it starts. So far they've more or less played the core races (if you include Gnomes, Tieflings, Aasimar, Dragonborn, and Half-Orcs as core races, which I do), excluding Grog the Goliath, Caduceus the Firbolg, and Nott the Goblin (who turned out to just be a halfling). Maybe a Warforged as an Aeormaton, Lizardfolk, or Tabaxi (can you imagine Sam or Laura as a Tabaxi? That would be great). Some classes that they haven't played before would also be great. Maybe Sorcerer, another Warlock, and/or possibly a Wizard or Artificer? I would love to see the dynamic an artificer would add to the table, with the team splitting the infusions and playfully bickering over who gets the magic items.
I would also love another official Critical Role 5e book, hopefully with a revised and official Blood Hunter class. Wildemount is one of my favorite 5e setting books, tied with Eberron and just above Ravenloft. More official content for the world could be great, especially if the next campaign takes place in another area of Exandria that was more or less unexplored in either Critical Role campaigns (maybe the Shattered Teeth, Marquet or Issylra?).