I really love to build my decks as thematically as possible, and one update that would really help this go a long way is adding in the printings of cards that are already in Arena, especially when that set is already in Arena. For instance, Bloodghast is now in Arena and legal in Standard, it would be awesome if the Bloodghast printing from the Lost Caverns of Ixalan Commander set was added too. The same is true for Canopy Vista, Clifftop Retreat, Explore, Black Market Connections and so on. A few cards from the LCC set are already in Arena so I would think that would make coding it in even easier.

LCC would be top of my list, but really, now that so many commander sets are including new art for staple cards, it would be great if they get added to Arena at the same time as the new commanders get added