99th Country vs Separate Server. Both are interesting.
99th Country allows you to take advantage of the entire player market, so you can acquire veterans who have skills.
Separate server would be interesting because everyone would start at zero, with no pre-trained players. It'd be like the first season of BB. Every player would be awful. A big gameplay risk is whether the economy would have enough users to be stable. If there's not enough activity, the economy would be incredibly volatile. One cool aspect: Ever wondered if you're a better manager than that guy who started in season 4, but he's just been playing so many more seasons so his team is more built up. Now everyone starts from zero, so you get to see.
I actually think Separate Server sounds like a lot more work. Marin (or whoever) would have to run dual worlds. Dual weekly games, dual offseasons, etc. I don't know what it takes to run BB, but I thought a 99th country is much easier.