Originally Posted by Ussnorway
I'm willing to bet patch 6 will be the last...
We know definitively this is not the case. Salo said that they're planning an enormous modding update in a few months a few days ago
Originally Posted by Salo
We are working on official mod support, and have been for a while. We want the very best for you, which includes establishing a pipeline that lets mod authors release their mods across different platforms.

Together with the platform holders, we are working on making this a reality, and are forming a team to support mod curation. We’re aiming to offer modding support for things like classes, UI, customisation, spells, and certain assets and game mechanics.

As this is no small task, we hope to introduce the initial stages of modding support in our next big patch, which is still several months away. Frustrated as you might be now, we’re keen to work with you on this - and have plans to reach out to popular mod authors to talk further and work together to avoid issues in the future.
This definitively means that there will be at least one more update but I strongly suspect that they'll also release "Baldur's Gate 3 Definitive Edition" likely afterwards. So if I had to guess there will likely be at least 2 more major updates.