I'd just like to back off and let nature take its course. I think people have good ideas here and either implementation would work, assuming the details could be pinned down.
ASSUMPTIONS
No movement control. Micromanagement is something that needs to be avoided, or the idea will simply never fly.
Trade routes are established in diplomacy or some other similar negotiation mechanism between two civs. Establishing them through movement is a no-no.
The trade routes would have huge implications for diplomacy, with people trying to get a few extra bucks by attacking a trade route, and people holding others responsible for when things go wrong. Is the person who attacked the route responsible? Is the person who was supposed to be defending the trade route responsible? Maybe both are responsible? One thing's for sure, raiding a trade route will be pretty fun
CHOICES
1. Build caravans or not?
Are they automatically generated when you establish the trade route, or do you have to build them, adding them to a pool? Either method has benefits, and I support either one. To me this is less important than actually having tangible trade routes once again.
2. Draw trade routes or talk about trade routes?
To me this is just an interface decision. To fill in a few fields with drop down menus would be satisfactory, but clicking between points on a map would be kind of neat too. Either way, this decision is important, just not important to me at this time.
3. Dotted lines or moving units?
I think this is one of the biggest talking points right now. Realism is a factor in both -- some people feel as though having units at a certain place and certain time is more real. Others feel that having a route that is covered quickly in the span of a turn is also pretty realistic. To me, realism should not be the question, but gameplay.
A dotted line is easier to pillage since you can be anywhere on the line, whereas hitting the unit is harder since you need to actually find it. On the other hand, a dotted line requires less computation, whereas moving 25 automated caravans could potentially be a resource hog.
Either one is cool with me, but in either case, you need to come up with a mechanism for the following question.
4. How do escorts work?
Personally, I'm a fan of combining the escort feature with the mechanism by which you create the trade route. When you create the trade route, each nation has a hand in building it, which includes supplying the troops for escorting. Whether it's a dotted line or a caravan, a limited number of troops (3?) are "bound" to the route. And whether you're attacking an automated unit, or pillaging a dotted line, you have to go toe to toe with the escorts before you can reap the benefits.
If your trade route is attacked, you would get a pop up at the start of next turn if you'd like to either pay to replace the escorts, or whether you'd like to put the trade route on pause. Maybe force a re-negotiation. Maybe force a multi-lateral talk between the traders, the nations through which the trade route passes, and the attacker.
Any solution is fine, so long as we can prove that there is at least one solution that doesn't make the whole idea fall apart.