I believe this “account switching” feature is set to allow support for switching between multiple profiles within all the client apps, desktop, mobile, and browser extensions (without the need for multiple browser extensions or browser based profiles.)
Currently this can be done via the client applications, but can be quite tedious.
Having to log out of the current account, set a separate self-hosted URL if needed, and then login with separate email and master password.
I believe this new feature will allow you to instead login with multiple accounts (and hopefully accounts connected to self-hosted URLs) and allow separate profiles to be switched between them without the need for multiple steps to logout, change settings, and login again.
Not sure if this “account switching” feature would allow for multiple vault entries to be combined into a “single pane of glass” so to speak, but I would argue some would find this convenient, while others would prefer to only have the accounts easily switched.