yes, there are many games built around various respawn systems. The big limitation right now is on join in progress, which is not supported (but has been promised for ofp2).
Well, actually, the other limitation is on mission design. As suave says, the OFP engine is like an operating system. well, it's a little more limited than that... but that's what makes it tricky.
Mission design depends on the units placed in there, so a mission is made specifically for addons and mods. For example, let's say you wanted to have some sort of vietnam scenario where the human players make up a LRRP squad on a mission to locate an enemy base. You insert via Huey 4 klicks from the search area, then hump it in. Once you locate the base, record the location, pull back, and call an airstrike. If needed, some M101s at a FB will prove a couple 105mm fire missions. Call it in, then withdraw to base.
Okay, for such a mission you would need:
a Vietnamese terrain (such as the 12x12km Ia Drang Valley map, or the 25x25km PMC Vietnam Map, or something else)
a set of vietnam-era soldiers and equipment (SEB NP2)
Some appropriate aircraft (e.g., DKMM's Vietnam-era paintjob OV-10)
The howitzers (CoC M101s)
Some effects scripts (say napalm for the OV-10s)
You would build the mission up specifying these units, and you can't replace them at game time. The disadvantage is that everyone has to have the addons downloaded (Tehre are some auto-downloaders that automate this process on some public servers), and installed. the advantage is that you can have addons that add entirely new features to the game through heavy use of the built-in programming language (such as my howitzers).
The problem is that, with so many factors in play, missions can go bad/out of balance quite easily, especially multiplayer missions, where designers don't always have a handle on what the engine does and doesn't share between clients (and how to work around these limitations). So when you download MP missions you get a real mixed bag: everything from MP free for all deathmatches, to capture the flag, to combined-arms CTF. to RTS games, to realistic cooperative missions, to BS coop missions. And you get stuff that works and stuff that doesn't.
The advantage of Suave's system is that the OFP mission environment allows an editor to develop a "one off" mission quite easily, and will even give the designer some surprises.
