Kind of takes away the Team aspect of Guns. A Free for All would just turn into a sniper fight, with everyone too scared to really engage.
No ally to help secure kills, no chance of reprieve from very difficult fights, snowballing combat, utter confusion (More so than usual at times), might end up being a mode more lamented than enjoyed.
I'll hop on the train though; Domination game mode? Except without the balloons as points, have the mining facilities, the armed ones. Make it difficult to actually cap points, and then require a team to take said point, to disable base defenses and cover for incoming enemy attacks.