As long as the story is well-written, and the gameplay is rewarding, I'm not sure the level cap matters much to me. Many D&D video games in the past have had either sequels or expansions soon after, so it woulld be a surprise if there no further plans at all.

But first, BG3 has to be well received and make money, otherwise there is little prospect of higher levels, toolset or DM mode. At this point, most of their decisions look like they are aiming towards their core audience rather than any massive expansion of appeal, and I would expect them to sell well to those that already like them.