Ability to Share All Vaults or the Ability to nest Vaults
Proton Pass sharing is a terrific idea but it only allows the sharing of one vault. I have over 500 accounts with login credentials and placing them in one vault is unmanageable regardless of the ability to search. I've got them separated by category in separate vaults. Sharing passwords with a spouse is important for me; I would like to be able to share all the vaults.
This could be solved by allowing vault nesting and share the root vault. Or allow sharing of as many vaults available to my Proton Plan.

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Anthony Pagano commented
I was wrong about this----the ability to share multiple vaults (at least with the Proton Unlimited Plan) is already available. When I initially read the Proton Pass documentation this was unclear. And the step-by-step mechanics of sharing one (or more) vaults was also unclear (to me at least).
So I just had to bang on it for a while until I learned that more than one vault can be shared with the Unlimited Plan. The Proton Pass sharing process is similar to the sharing of files using Google Drive. When the sharing party sends a share invitation for a vault a small "people" icon appears next to the vault name. The receiving party receives an email indicating that something has been shared,, but the invitation must be accepted by logging into their Proton Pass. At the top of the Pass screen will be an invite message with a button for acceptance. Each vault will have a separate acceptance message and button.
This was my experience with the Pass Web application. I'm not sure if things are different with the smart phone Pass app.
There was one limitation: Proton Pass didn't let me share more than 15 vaults in any given day (I had 43). After that it didn't matter where I or my shared party were logged in (computer or smart phone) we had access to all the password accounts.