Performance increase only does not matter for devs, DX9 should be long dead if so, we also whould be using more Linux and OpenGL as well.
no offense but if dice can pull it off they crytek and unreal can do it haswell
and then that is a majority of pc games and console ports...
Not gona happen as long you still need to target DX/OpenGL alongside it, and "mayority"? nope, consoles does not count when doing a pc port, PC hardware and market shares count, with that in mind you gona still be targeting mainly DX and/or OpenGL, at that point Mantle is just a "extra weight" to carry along. I dont see anyone using it unless AMD pay them, its even worse than Physx.
If we are talking about a Mantle only port things will be diferent, but that not gona happen unless GCN gets +75% of PC market share. Again consoles does not count when you target PC.
Thats is the part where the AMD argument of "makes things easier for devs" fells apart, even if you game is console only, and it runs on Mantle on console(still not clear about it), if you gona do a PC port, you have 2 options, do it Mantle for 15% of the market at best or do it DX for 100% of the market, if you do both, them Mantle is not advantage for devs.
You even stopped for a moment to wonder how less buggy could BF4 be if they have not wasted time in mantle at all? Do you know development times? We are not even sure if they need mantle for console version at all...