This seems to be a feature request as per comment #0. hence, marking it as untriaged for further inputs from dev team.

Thanks...!!

We've discussed UIs that make the MRU ordering among the tabs clearer.  However, in the end, there have been relatively few scenarios where this information is critical to users, and the meaning is often challenging to convey (it's not obvious that the different states are anything other than visual bugs).

The most common case where something MRU-related is useful is when trying to toggle between two tabs.  In this case it's less critical to _indicate_ which tab was used recently and more critical to provide an easy way to toggle to it.

So it's not a bad idea to think about this stuff, but I encourage framing the thought process this way:
(1) What specific use case are you trying to make better?
(2) In that use case, what's the core problem users have, that the current UI doesn't address well?
(3) Ignoring the current UI, what are some potential ways to address that core problem?  What are their pros and cons?
(4) Given the couple most promising answers to (3), do they mesh with the current design?  If not, what would it look like to migrate to a UI where they did?

The common outcome of the process above is that you don't wind up with any really great changes to the existing system, unfortunately.

(Mainly starting with a work related and one play related tab, we click
lots of "open link in new tab" links.
Now we have 4 work related and 4 play related tabs, all seemingly mixed together.
Yes we should have used separate windows...
Anyway true, in the end any effort to help the user automatically
organize them would mess things up for other users probably.)

Workaround: use shift- and ctrl-clicking to select the various tabs that are related to the same purpose, then drag them all out into their own window.

(Yes, I'm just thinking about the case where users haven't reached that point yet. I.e., not yet too crowded.)