The online indicator by itself was rejected, and is on the rejected suggestions thread, but I have a new idea: in Account Settings, there could be an “online indicator” option which controls if others can see if you’re online or not.

How does this solve the problem of not being able to help with the core functionality of Scratch?

It doesn’t help, but it doesn’t harm either.

Rejected:

TOLORS wrote:

8.3 Show when users are online
This suggestion refers to some sort of indicator that lets you know if a user is currently online. The Scratch Team has discussed it and has decided that it is not something that can benefit the core functionality of Scratch as a creative platform. Between making projects, sharing projects, and viewing projects, an online indicator is not much help in these areas.

Basically, it's a pointless feature for the things Scratch tries to accomplish, and as a result there isn't a reason to spend dev time making it.

If you can make it relate to the coding part of Scratch, then it would be fine.