+1 for Nested Vaults or similar functionality
This would also address the need to synchronize and collaborate with others on one vault, but keep a personal vault of notes one-way linked to the collaborative vault in a separate, local-only vault. (For example, think of a knowledgebase collaboratively built by a team, and personal notes on the projects, people, etc. in that vault that should not be included in the knowledgebase, but that need to link to it.)
I am interested in a similar solution: could Obsidian load more than one vault concurrently? Thus, rather than nesting a vault, multiple vaults could be used in parallel. There are definite downsides to this (e.g., interlinking only works when the same vaults are open), and it might not be a superior solution to nesting, but perhaps it could overcome some of the risks of nested vaults.