Let's not forget about the main purpose of an advanced, secure, email managing service ... I need to point this out specifically creating a new ticket about it:

FIRST POINT:
With all of the Proton Pass and Proton Mail cross-functionality being either completed or in development, it's also very important to still properly indicate what's going on behind the scenes and how SL / PP aliases are being used in ProtonMail, with ample icons, descriptions, indications, reminders, warnings and other signs available for advanced users.

Many people ofcourse look for sheer conveniences and just want everything done automatically, I would advise to take a pause and rather figure out to do this considering all aspects of User Experience and to not create other issues or possibilities of confusion.

Sorting and managing email is a big deal, let's remind ourselvs that this is one of the main reasons of being a subscriber to such a service, isn't it? It's all about added features, advanced filters and tools for efficient and timely management and organization

While there are many valid methods of organizing and sorting email, not all of them would care about my specific point, but in my case, what I came up right now, is that I use around 5-6 hard addresses for some key communication with trusted contacts, and then several HME pass aliases for various shoppings and other services that are in my opinion more likely to get compromised, ... for the hard addresses I sort them based on the address, for aliases I use topical grouping, emails from several different aliases which are related or similar field go to a particular folder, as there is diminishing returns of having an overly complicated organization. I figured it would be less practical to have each alias be put in it's own folder.
Anyway during ... ... .. I don't want mixups or any potential of either sending with a wrong address or inadvertently exposing who the alias belongs to, so there should be ample indications,signs, warnings and icons in the Proton Mail GUI to show that aliases are being used, including searching and filtering (thus sorting) by aliases and even perhaps reverse-aliases.

SECOND POINT:
Proton should consider ... now we have:

Proton Mail Additional Address or Alias
Proton Pass Hide-My-Email Alias
Simple Login Alias
Reverse-Alias, which doesn't apply to normal PM addresses
etc

It's perhaps getting confusing which "alias" are we're talking about even when we know about the topics. When Proton Mail was created, it was just Mail, no Pass, no SL, so I think it's good if serious consideration is taken to revise the terminology and find some distinct descriptions of all of these aliases.

I personally thought to use the term "hard address" for a PM "additional" address, dropping the "alias" altogether there.

I didn't spend too much time on figuring out the terminology so far, posting this and letting community chip in.