Would it be possible to link many accounts from different instances together? I may have 2 or more accounts, each in a different instance, but I'd like for people to know what are my accounts in each instance.
Would also be cool if optionally Follows are shared between them - This is, if I'm following someone in my account in instance A, then my account in instance B also follows it. (but not for followers... Well this subfeature would need a bit of a thought)
PS: My use case for having accounts in different instances is that I want to have one for each "environment" I want to browse on - One instance has the people who speak my language, another has people with my music interest, etc, etc.
I don't think anything is stopping you from just:
Each of your accounts can be browsed in its respective tab, or you can connect them to any application that supports multiple accounts on any platform.
Currently we don't have this feature. However, as we can redirect an account to another (see below pictures for where the setting is under /settings/profile), it wouldn't be impossible to add something like this in the future.
I can however not answer if we will, at this point in time.

Account redirecting is technically for pointing one old account to a new one, not running two separate accounts.
Anyway, I'm still not really sure what additional functionality this issue is requesting. I can put, for example, @[email protected] in my bio on @[email protected], and vice-versa. I can follow the same people (or different people, or whomever) on both or either account.
The only actionable thing I see that isn't already possible in Mastodon is to have one account automatically follow the follows of another account -- which seems a bit niche when you can manually follow someone twice, if you wish.
My request was just general - it feels weird to have many unlinked accounts in a social network that's uncentralized.
I didn't think of just putting this info in my bio, so my main use case is covered by updating that.
In some way I think it would make a more unified decentralized platform, but it's true we have easy and fast workarounds for the simple use cases it would cover. I'm happy to close this Feature Request