Mainly the ability to flag planets with P1, P2, etc, but yes.
What do you imagine this looking like? A simple "P1" or whatever number next to the planet on the map, the planet changing colors, or something else entirely?
Hmm hard to say, i hadn't really thought about it yet. I would say that the key is to keep it simple, yet not too limiting either. This is something that should remind you in an instant what your priorities are.
In AIWC, different people used the priority system for different purposes. Some people used it to see quickly what their next targets for conquest were, others used it as an indicator of how dangerous that planet was to them, etc. The old system worked great for many uses.
I however, am one of the people who used it to indicate where certain capturables or nasty AI structures were and simply remember which number i assigned to which object. I basically used it as a marker to highlight what i needed to keep in mind. The SuperTerminal was P0, Datacenters were P2, The ARS were P8, etc. The same numbers were always assigned to the same objects in any of my games. This helped me formulate strategies a lot quicker, but there were a few problems with it.
First, there were not enough numbers. The priority system only had 10 different numbers and the variety of capturables and nasty AI structures was simply a lot bigger. I could have used at least P0-P20, possibly even more.
Secondly, many planets had multiple objects that i would assign a P number to, and we were only allowed to assign one number per planet. "What is a priority to prioritize?" is a question i often asked myself. Maybe my way of playing was just silly.
For my personal preference, i would suggest to use the P system again, only expand on it. Allow for higher numbers, and also multiple numbers per planet. My imagination when it comes to what something is supposed look like is rather poor, but i imagine it would look something like this:
P 23, 8
or
P (31, 19, 3)
Something like that. I would suggest to put the P number(s) right above the planet image or right above the name of the planet if your planet names are always on. Below, left and right have numbers there already but above is still empty. Will be up to the player if they want to clutter it with more numbers or not. I certainly would.
As for colour, I would keep it simple and plain white. I feel like this game has enough pretty colours to distract you already. I can't speak for others, but the colours of the P system in AIWC did very little for me. The numbers were more important.
I would consider the planet changing colours a bad idea. Not everyone is able to see different shades/colours well, if at all. It would look cool, but it would diminish the usefulness of the tool, in my opinion. You could always add some sort of colour customization to it, if you want to give people that kind of flexibility.
Bottom right (or bottom middle) of the Galaxy Tab screen would be the perfect location to put the P system menu icon (or whatever you plan on using) in my opinion. It doesn't belong in the Sidebar since this would a Galaxy Tab thing only. Maybe right next to speed up/speed down icons.
I have no ideas for something else entirely, sorry. I am usually better at thinking of ways to improve what already exists, than create something new entirely.
I don't know if any of this is what you guys were looking for at all. Maybe I'm the only weirdo who used the Priority system like this. Still hope it gave one of you an idea.