It was a joke, mostly (hence the ). The part that was not a joke was 7 years of experience with exactly the sorts of mods you're talking about.
The vast majority (I'm talking 95% here) of big mods never get done. People have cool ideas, and sometimes they get other people to agree that the ideas are cool, and once in a while they manage to do actual work. But, in the end, most are brought down by the fact that people don't realize how insane a province mod, TC, or similar mod is. I suppose I should give actual advice.
1) Know exactly what you're doing. Write a design document, or at least a detailed outline of your mod and everything in it. You can't just say "I'm going to make Highrock," you need to know the sorts of people who inhabit Daggerfall before you ever set foot in the CS. Make these plans available for people to see.
2) Make a detailed plan of action. What are you modding first? Who is modding what? Prioritize, cater to your team's skills.
3) Never rely on others to do your work. If you really want a mod to get done, you have to be willing and able to do it yourself. If you're working in a team, plan on the fact that people are going to disappear. Establish some sort of procedure for disappearances so you don't loose all their work.
4) Be realistic. If you know nothing about modeling, you probably shouldn't plan to make a mod that features thousands of new models. Even if you have a modeler on staff now, he may be gone tomorrow.
5) Don't expect help, at least not at first (and probably not later, either). There are hundreds of people with cool ideas, and most of their ideas get nowhere. You need to convince people that yours isn't just another dead project in the making, and that takes time and effort.
6) Be prepared for long hours and frustration. I like to joke that I've spent more time fixing Hammerfell than I have making it, but its absolutely true. I've gone through 400+ cells by hand to delete a grass texture or two. I've had to remove 800+ flowers erroneously generated by the region editor. Tamriel Rebuilt (which I led and modded for for years) has redone all its landmass thrice over, discarded more work than most mods ever produce.
7) Establish some sort of team hierarchy, make sure everyone knows what they are responsible for, who to ask for help, etc. Make sure you have a way to communicate, discuss ideas, and share work.
8) Make sure you really, really, really want to do it.