Yes, I've played a little Tribes before
The SS/CS distinction is a double bladed sword imo. It's cool that you can make seemingly endless variations of the base terrains/interiors... without having clients need to download anything out of the game..
But that makes CS maps, with new interiors/terrains/textures etc, very undesirable to players. Who wants to exit the program and download maps when you can play on an endless variety of SS maps? A lot of newer players probably had no idea the distinction even exists, and just assume it autodownloads all maps. This makes designing a truly custom level not very desirable, as it will likely not get played very much, if at all.
The only CS maps in rotation on any populated T1 or T2 servers are those that are officially sanctioned map packs (Open Call T1 maps, Classic Mod maps in T2), or map packs embraced by the competition community (Xpack & XPack2 in T2). There were TONS of awesome client side T2 maps that NO ONE played because of the SS/CS bs.
I think without the Server/Client side map distinction that Tribes Vengeance will see the kind of truly awesome custom levels and mods that nearly every Quake/Unreal powered game communities enjoy. People will likely put a lot more effort into their maps and mods, and we wont see so many of the lame SS mods and SS maps that do no more than add tons of weapons, or move around a few bases.
Just my $0.02