it'd take allot of work. it's one of the things that dman and i talk about, torx engine has the best distance/lod handling i've seen, but the serious 2 engine is pretty damn slick with theirs.
i never gave it that much thought except for distance culling stuff for entitites. takes allot of math to do that sorta stuff, and with wf's entity load (its pretty damn large) it was never really an issue or a goal, past maybe 4x the size of a team arena terrain map.
just don't have the time to make the maps to fool around in em either. oh it'll hold a large heavy map, i got 6 TC maps pasted into one with allot of stuff opened up that was formerly closed, maps like research district and urban assault (part 2), takes a day to compile, takes 512 megs for a server and a client locally, but it works. i'm gonna release a tech port of the base engine that will just hook into tc stuff with that huge map. that's all it's gonna ever run, one large map, but its kinda cool cause the ai works (bspc's aas crashed q3).
but for call of duty or unreal-ish engines with outdoor terrain, i like tribes2 physics with vehicles and i don't think i could write it any better or would even want to try; i'd rather be playing it.