This hypothetical scenario i'm referring to is a FLOSS Battlefield clone. Most FLOSS FPS games are arena shooters, so seeing a teamwork oriented FPS with vehicles that's open source would be an interesting change of pace. Hence asking about megatextures.
Quake Wars is a idtech 4x teamwork oriented FPS with vehicles and improved megatexture tech, is not FLOSS tho.
This hypothetical fps would need the following qualities:
Free Libre and Open Source: Self-explanitory
idtech 4 is GPL so is open source but is not libre.
Multiple Architextures: It should run on any architexture as long as the mimimum system requirements are met, hence asking about replacing the dll system with something like qvm or PNaCl.
idtech 4 runs on x86/x64, MACOS and Android (for android you need the ported engine not the original one tho).
Low specs: The main goal is a Battlefield clone that can run on most modern devices. The graphics will probably be low poly cel shaded, so that the graphics look decent on newer systems yet can run on old ones.
original idtech 4 not BFG can run just fine in directX 7/8 type hardware that is very old.
Multiplayer: Up to 64 players.
Afaik not possible without changing the vanilla multiplayer code but i'm not sure.
Map Format: Must be optimized for large outdoor maps. Hence asking about Megatextures. Of course, looking at another engine, like one of the Cube engines, is an option... again, this is all hypothetical.
idtech 4 is not optimized for large outdoor maps, they are possible but making them is very hard, the editor doesn't even have a terrain tool, nor a way to easily "plant" objects in the terrain surface, and optimizing them is very hard as well, vanilla idtech 4 lacks even a simple LOD system and terrain streaming plus vegetation rendering is very basic and imo ugly, is no Cryengine that's for sure.
Physics: There will be ragdolls, things jumping off airplanes, tanks... having simple Quake 3 esque physics won't cut it.
idtech 4 physics are surprisingly very advanced not Havok or PhysX like but much better than the Quake 3, ragdolls and vehicles are perfectly possible without changing the physics code.
Internal VOIP: Battlefield 2 allows for voice chat for teams, squads, and commanders talking to squad leaders. Obviously that will be needed here.
Afaik doom 3 has voip but i never tried it.
Theme: The characters will be robots. This is done for several reasons:
Robots are perfect for idtech4 the normal maping tech plus the in_game GUI surfaces makes for very complex and fun robots, human charactgers is where vanilla idtech 4 lacks but for cellshading is fine, you need a cellshading ARB shader tho.