When debugging a Mendix applications that have many submicroflows, it can be challenging to flow execution flow and you quickly end up with dozens on tabs open in the modeller. You can loose you place quickly and if you need to go back a couple of steps, can be tricky. What would be really useful is an execution plan interface (kinda similar to an SQL Server execution plan) so you can see you execution flow, but be able to click on objects, and see where you are within it. This way, if you need to go back a few steps, you can just refer to the diagram and see where you came from.
You have my vote.
You are aware that you can switch tabs using ctrl-tab? This does help a little.
Or even if the tabs up top were in order of when they were last opened would be really useful. Anything to make it so you can easily go back to microflow or page you were just working on.