You can probably build some understanding from these threads:
Visual scripting roadmap update - August 2020
Visual scripting roadmap update - September 2020
November 2022 Visual Scripting Update
Key words are “high performance interpreter” and “Graph Tools Foundation”.
A lot was discussed in the official Discord server for Bolt/Visual Scripting but Unity stopped all comms there last year around this time and Discord is a pain to search.
Long story short, basically no new features have come to Unity Visual Scripting since 2020 besides sticky notes, and a very rudimentary new Input System support. In all other respects the tool is practically identical to Bolt 1 from the asset store as it was in 2018. All the improvements they’ve been working on for the past three years such as the high performance interpreted runtime and Graph Tools Foundation (UI Toolkit based) graph framework have been internal only.
The reason why I’m believing they’re doing a rewrite is because they’re not shipping incremental improvements to the current version of the tool like they originally intended to. But it might as well be that they simply don’t want to do double the work for current IMGUI based UI implementation and the upcoming Graph Tools Foundation UI implementation. Still, they talked about reworking/improving variables management, custom event management and many other things that would require fundamental design changes even if we disregard the new runtime and the new UI frontend.
All of this is happening behind closed doors with practically no communication here or elsewhere. They’re working with studio partners with this so we can only guess what’s happening from past discussions. It’s also unknown in which Unity version it’ll finally ship. It’s very unlikely to happen in the Unity 2023 cycle. Might be Unity 2024.
EDIT: Here’s one excerpt from Discord, yellow named people are official Unity employees or were at the time at least:
