Turn Nexuiz into Far Cry like game, possible?

[Alien]

DP (darkplaces - nexuiz engine) can do much more, than orig quake. It lacks some q2/q3 support, but it also has more advanced things than latter one. Check DP readme.

[HarryButt]

I don't know about outdoors with DP...
If you look at the first Onslaught map and all the fog and stuff... I don't know, but it seems to me that DP is not comparable in any way to Crytek's engines, which made outdoor levels actually run better than indoor levels This is not the case with DP afaik.
I think idTech4 is a better comparison and the only game with really massive outdoor levels, I can remember is ETQW, which didn't perform as good on my iMac as indoor games like D3 or Q4.
I don't say, I wouldn't want a few outdoor levels, just for diversification. But you can't expect the large scale of FarCry-maps with DP.
You should ask sev for ideas though, since he seems to be the guy for tropical adventures He's building a new map atm.

[Alien]

http://www.modwiki.net/wiki/Visportal technique is used in quake engines. Outdoors are visualised like:

These are created with the "textures/editor/visportal_distance_*" materials. These portals will fade to black or to an image specified in a custom distance-visportal you create when the player is x units away from the portal and will close when the player is y units away from the portal, whether or not the portal should be open according to the general visportal rules described above.

I think, that this is only used in idtech4.