Can an option be added where we can star and/or flag a message and message thread for follow up, and/or mark it as important please?

I know that messages can be pinned to the top, but there doesn't seem to be an option to flag a message for follow up, or to star it as important, even without pinning it to the top.

Custom flags, can be used to prioritise messages, and set an expiry date, or a deadline.

For example: right now I am sitting in a waiting room at the doctors, and a message has come through which I need to follow up on, but it's inappropriate to reply or follow up until I get home. It also doesn't need to be followed up today, but it will be in a couple days, so I would flag it as important, and to be followed up on by Monday afternoon. Another message has come through that needs to be replied to urgently, but I have to check something at home first, but I have to follow up before close of business today.
Another message has come through which is very important, and must be kept, but doesn't need any reply.