Thinking more globally about off world resources, is the idea of a popup when you build a landing stage even the right one?
Well, I think it works fine. Simple is good. And I think tweaking the choice text strings a la "Sardaukar cooperation (superior assault troops)" would work fine as an explanation.
My concept of the ginaz unit was that it was a *single man* who could make a huge contribution to a battle.
I don't think this is right. No single man makes any significant difference in a fight at the scale of hundreds->thousands of soldiers that we're talking about. We aren't representing skirmishes here, we're representing war, like at the scale of the Harkonnen invasion of Arrakis (which I think is on the order of 200,000 soldiers? I may be misremembering though).
I think that what we're representing is some elite units who have had their training from Swordmasters (who in turn were trained at the Ginaz school). So, if you get the Ginaz training resource, you now have some swordmasters as part of your retinue, who can provide some elite/high level training to your soldiers.
so perhaps the promotion would somehow remove the unit from the game for some time.
This doesn't sound like fun to me.
I wonder whether Ginaz training might be cooler as a Melee unit promotion you can only get if you have the Ginaz offworld resource.
The way I would envision implementing this is to have a string of superior resources that required the resource.
Ginaz tranining 1 = +10% strength, +10% vs melee units.
Ginaz training 2 = +15% vs melee units, 80% resistance to collateral damage
Ginaz training 3 = +10% strength, immune to first strikes
Or something like this.
Maybe the promotions could also have a level requirement, so only level 2 units could learn Ginaz training 1 for eg.
Why would there be a world limit? If we have reached the world limit, what is the reason that another unit cannot get the promotion?
Combination of balance and fluff. We wouldn't want the resource to be too powerful, and we wouldn't want to lose the feel of this being something elite, rather than generally available.
Remember how Duncan Idaho, Gurney Hallack and Thufir Hawat have trained a small handful of Atreides forces to be as good as the Sardaukar. That is what I think we are trying to envision here.
I'm not sure how feasible a national cap would be if we made it a promotion though; if we want a national cap I think we need to stick with unique-resource units, like the one we already have.