Allow tags for context

This is an idea still to be refined; ideas are very welcome.
When I am at work, I want to use work-tagged rooms - so if I click on some room member in order to get a direct chat, I want to be brought to the direct chat tagged 'work'. If I am in a room tagged 'leisure' and go to the direct chat with the same person, I want to be brought to the chat tagged 'leisure'. That way, different concerns don't mix up, and I don't have to go chasing for the correct room to use.
There are various ways in which this could be brought about:
- Some tags could be labelled 'context', and when starting a direct chat from a room with context tag(s) X, the direct chat with the same context tag(s) X is selected (or offered for creation, if nonexistent).
- Per room, room members could be associated with a specific direct chat. This is more flexible, but also more work to set up. Maybe the context tags could be a default, and specific association used for refinement.
- A context could be set explicitly (as a community, or a filter on the room list), and selection of a direct chat room would be restricted to that context. This has the advantage that it is extensible beyond 1:1 chats - if within one context I attempt to address any group of users I'll get a room within that same context. (How to tell Element that one wants a chat with users U1, U2, .. is a separate issue - there are some obvious choices, such as checking people in a room member list, but they may not be optimal.)

This would allow for a well-enforced separation of contexts, which can be quite important:
- For sensitive information: someone X might be willing to let someone else Y read the contents of one 1:1 chat with Z, or even invite Y to join, while being definitely unwilling to share information from another 1:1 chat with the same Z.
- For mood reasons: X may reprimand Y in one (e.g. work or school) context, without wanting to spill that to another (e.g. leisure) context.
- For organisation: X may want to keep all information regarding a certain project together in a to-the-point chat.

Both more use cases and more possible implementations are not hard to think up. I am not sure what would be the best implementation approach.