Have you specifically chosen “register” here, as in “registration”?
From the broader context I would rather say you are talking about “authenticate” / “authorize” here.
Authn. would basically be OpenID; authz. maybe OAuth.
I sounds like you are referring to an application where you would put your three accounts and the application would decide where to send your content.
I assume you don’t like that idea; neither do I.
I think I understand how you come to this conclusion, but what you refer to “identity” here from my point of view is not the problem, although identity in the actual sense is related to it.
I cannot really make out what I would call what you are referring to, but let me shine light unto this from a different angle.
There are other problems underlying yours.
Basically, I would say it’s a problem of channels.
You used “media”, but in my opinion it’s not about the medium but the structure: short text? still images? gifs / short videos? – its all different media, but the same channel type, micro/image-blogging in the preceding case.
Imagine an Internet Entertainer.
Your main channel might be non-short-video where you play sketches, talk about news, explain things.
But you also have secondary channels; for example micro-blogging to share short thoughts about the world.
To reiterate already, the difference between the channels to me is not the medium, it’s the structure:
The main channel will have lower quantities but higher quality; e.g. one scripted sketch a week.
The secondary channel will have much lower quality but way higher quantity; (look! doggo!)
You can also say that you can reach different kinds of audiences on the channels; there might be more people who are fully okay with just your main channel and are not very interested in the rest; so they don’t follow the secondary channel. Would there be only a single channel, you would overwhelm the people just following your main content very easily, even though you are also happy to share/connect more.
Internet Entertainer might be an “extreme” example, but it helps visualizing it.
Now, in my head the problem you are experiencing is because this concept of “channels” seems to be missing awareness.
The current state is that instead of establishing new channels, completely new networks are established.
Mastodon for micro-blogging, Pixelfed for image-blogging, PeerTube for video.
They all are network and channel at the same time.
Wait, networks? We didn’t define that yet!
To me both networks and channels are between identities; but channels are 1:n while networks are n:m.
from our example there are two channels (e – Internet Entertainer)
- e:fv; fv = main channel (i.e. video only)
- e:fm; fm = secondary channel (i.e. micro blogging)
and one network:
- e:f; f = all followers
in the current state of the fediverse, w/o channels, this can only be represented by two networks, i.e. two accounts:
- ev:fv; video
- em:fm; micro-blogging
So, how to resolve this then?
Basically, this would require the current projects to consequentially separate network and channel.
The target state would be that you only have one network (account) on one instance, e.g. mastodon, and have multiple channels on this and other instances (mastodon microblogging, pixelfed imageblogging, peertube videos).
Oh well, this sound very much like your initial suggestion, just differently framed?
So far, so good; more next time, I’ll have to see what to make of this until then.
(As you might have seen, I love solving problems by introducing auxiliary concepts.)