I would love to see an entire franchise around BG , and D&D in general. If BG3 plays as well as it looks already I would be for expanding Larian to handle multiple vertical projects similar to how Marvel has regular releases to their movies.

Things I would love to see

Yearly or bi-yearly DLC (expansions to story and increase levels)
GM/DM mode
Sequels

+

Using the same engine would like to expand into new stories perhaps stand alones.
, and perhaps even new realms (i.e. Dragonlance etc.)

The games are as endless as the tabletop