Your map looks great...
I had an idea like that,
GDI have to assault Nod
GDI - Hovercraft + planes, start in ocean with WF etc
Nod - 3 Obis, 1 guarding each corner and 1 powerplant in the middle of the 3 : )
Stuff like that but not going into detail : )
You need at least a HoN to make Infantry Barracks work and vice versa. Don't ask why
Still, a turtling survival map would be interesting, but not made for Marathon. We just need to find a way to make sure Nod players are always at the top score than GDI's, so when the time runs out, Nod wins... or the other way around.