The idea is utilizing how the AI engine loops within a state like OpenGnd0, for example.

By making a variable loop from 20 to 0, and resetting at will, the Queen can be ordered to move between the two bases.

Having a third base may not work with this code. But as a prototype, this is somewhat a good start.

Here's the code used to order the Queen around:

void CommandQueen(int player, int CTown, string StructHatch){
order ord;
point OTarg;
unit Queen;
unit nearbyHatch;
region r;   
       
        nearbyHatch = AIGrabUnit(player, StructHatch, c_prioScriptControlled, AIGetTownLocation (player, CTown));
        Queen = AIGrabUnit(player, c_ZU_Queen, c_prioScriptControlled, AIGetTownLocation (player, CTown));
        r = RegionCircle(UnitGetPosition(nearbyHatch), 4);
        //OTarg = UnitGetPosition(nearbyHatch);
        OTarg = AIRandomSpawnPoint (player, r, 50, 100, 3);
       
            ord = AICreateOrder(player, c_AB_Move, 0);
            OrderSetTargetPoint(ord, OTarg);
       
        if (UnitOrderIsValid(Queen, ord)) {
            AICast(Queen, ord, c_noMarker, c_castHold);       
        }
        else {}
}

Here's how it is used within OpenGnd0:

        if (loopTimer < 20 && loopTimer > 10 ) {  //queen management prototype
            CommandOvie(player, c_townOne);
            CommandQueen(player, c_townOne, c_ZB_Lair);
            CommandQueen(player, c_townOne, c_ZB_Hatchery);
        }

        if (loopTimer < 10) {                    //queen management
            CommandOvie(player, c_townTwo);
            CommandQueen(player, c_townOne,c_ZB_Lair);
        }
        if (loopTimer < 1) {
            loopTimer = 20;
        }

Obviously, this can be developed further. And as you can see, even if c_townOne is used at both cases, the queen will still be ordered to move to c_townTwo.

I have no idea what's going on with that.

Obviously, this can be developed further. And as you can see, even if c_townOne is used at both cases, the queen will still be ordered to move to c_townTwo.

I have no idea what's going on with that.

I think this might be the culprit:

OTarg = AIRandomSpawnPoint (player, r, 50, 100, 3);

Those 50 & 100 values set a min/max distance from the enemy.  What happens if the minimum distance from the enemy can't be reached within the region you specified?  Will she move outside of it (and towards your natural expansion by default)?

I'm interested in this because I want to learn about what kinds of unit management functions we have, but I don't actually think that shuffling a Queen back and forth from Main to Expansion is very useful.  She can barely keep up with spawning larva at one Hatch, and when you add travel time and the possibility of losing her in transit it doesn't seem worthwhile.

I could see performing one time reassignments - you might start a Queen for an expansion before it's Hatch is built and then just send her over, for example.  Or she might flee a dying expansion and be used for healbot duty until a free Hatch was available that needed larva.

I'm also interested in trying her out as a battle healer.  She could be a key part of a Nydus drop, coming out 1st and keeping the canal exit healed until the army can get out.  She would also be devastating as part of an Ultralisk raid - her healing combined with their damage mitigation would make for a very long lived assault.  Her speed would be an issue though - you'd probably want Overlords and/or a Nydus canal to facilitate her transport and to serve as a shelter if she gets targetted.  I think healing duty queens might be valuable in other circumstances too - anywhere that you have expensive units really - Guardians, Infestors, Mutalisks.  Particularly in a heavy air battle scenario where minerals are plentiful and gas is scarce.

We would need to make significant alterations to her Tactical AI to assess whether she was part of a Hatch/Queen pair or assigned to a wave as healer.  I'm still learning about waves etc. but I think it will be possible to code.