Adding the ability to filter is great, HOWEVER, please be careful not to break the typical existing use case! I found out about this change because my Outlook happened to update to the new room finder suddenly, and randomly only two of our room lists are now accessible, even under the two different cities.
I have since added city information to all the rooms and I assume this will fix the problem once the change filters through, however, this could have caused us a major problem for booking our car fleet (they are set up as room mailboxes) if it had happened to roll out to all our staff at the same time it rolled out to me. This would have had a real impact on the lives of vulnerable members of our community.
Whenever you're designing a change to a system, make sure that the typical use case works (i.e. the ability to see all room lists easily and select the rooms from within them) before rolling it out!