It is a rather fundamental change though - it moves conversation system from “avatar” speaking to party speaking and new systems would needed to be develop to support it both in single and multiplayer, alongside potential changes to the content of the conversations.
As just an average gamer I don't have access to specific information about Larian Studios' development team and their resources. However and like you said, implementing a party-based conversation system in a complex RPG game like Baldur's Gate 3 could be a significant undertaking and likely require a considerable amount of time and resources.
Developing a party-based conversation system would involve designing new UI elements, implementing new dialogue logic to support multiple characters, and potentially revising existing dialogue content to accommodate new party-based interactions. Additionally, implementing this feature for both single and multiplayer modes could further increase the complexity and time required for development.
Based on similar features in other RPG games, and assuming a team of experienced developers with sufficient resources, it could take several months to a year or more to implement a party-based conversation system in Baldur's Gate 3. However, without knowing the specifics of Larian Studios' development process and resources, it's difficult to provide a more accurate estimate.
That being said, if this has indeed been a requested feature for many months in a row, perhaps even since the beginning of the beta in October 2020, they could, in theory, have been working on it in secret since then. Fingers crossed
