Technically, you’re already using multiple vaults. What the second vault is or its purpose can vary depending on the user’s note system. I currently have four vaults—three of which I use actively, and two of those I use very actively. Honestly, I’m getting much better results compared to when I used to combine everything into one vault. The fact that each vault can have its own visuals and plugins provides a lot of freedom.
The effective use of notes across different vaults is theoretically possible. However, in practice, developing this further depends on the Obsidian developers. If this issue significantly impacts your user experience, you might consider opening a new thread. Referring to this thread in the new one could be a great contribution, allowing other users to see this topic as well. Have a nice day!