It is important that co-op players be able to help each other out; since we can already transfer control of metal/crystal producers that's the lion's share of what is needed, I think. It would also be nice to be able to do one-time transfers of a chunk of metal and/or crystal because even if you give the lower-resource player an additional 100/sec production they may need more resources _right now_. While caravans and/or trade posts may provide more interesting leads into other features, I think the best way of doing this is just a little sub screen listing the other human players and you can do some sort of click on a player name to bring up a box with "amount of metal to send" and "amount of crystal to send" fields and a "send" button. Instant transfer, 10% tax or whatever. Simple both for players and programmer (hopefully).
Yep, totally with you, I think this is the basic idea of what I'm going to do (probably no tax at first). This will probably be implemented through buttons on a new Trade Post unit, though, simply to keep this as part of gameplay and to avoid having yet one more interface button for something that is not that commonly needed.
The caravan run idea may be nice if it was more of a "commerce bonus" economic feature, so you could have this merchant fleet operating on its own and it's in your best interest to protect it (single-player or co-op, doesn't care). Could have the program auto-generate the freighters from planet to planet, and every time a freighter makes a stop it increments some local bonus counter (resource production, build rate, "happiness/morale" meter for the residents of that system, etc). I'm not sure if this fits in the military/naval scope, but it could give the human empire a more "alive" feeling.
Yeah, I've seen this in the earlier AoE games and also in RoL (and maybe RoN? Can't remember), and I really liked that. I think it fits with the military focus pretty well just because it creates new strategic opportunities and problems (we can get a resource bonus, but we also have to protect these new things).
You have some really good suggestions there. Here's what I'm thinking right now, for caravans (let me know what you think):
Caravans would be something that you could have the Trade Post automatically build from a queue, as you would with a space dock, so that you can either just build one or a couple of them, or you could have them be automatically replenished from a queue. Each caravan would have some moderate cost to it. I'm thinking that the pop cap for caravans would automatically increase based on the number of command stations you personally have (I really like this from RoL: number of caravans - number of command posts minus one). The caravans would move about through friendly planets at random, giving a temporary resource production bonus to each command station they visit.
There would need to be some sort of bonus for going longer distances, some sort of incentive for visiting allied planets perhaps, and some sort of reason for visiting more than just two planets in general. I'm thinking that maybe they would be required to visit something like 5 or 6 planets (or however many allied planets there are, if there are fewer than that number) before they could loop back around to the start of the planets and start over.
Anyway, that's what I'm thinking right now based on the ideas you posed. This won't be a real short-term feature, but maybe in the coming weeks. Hopefully the Trade Post will be more short term, although I don't know if I'll have time for that for this week's DLC.