My opinion: That's completely fine, as long as 16m Guilds don't start to look down on the rest and vica versa (On my server the usual response from them is "You killed XY boss? Tell me how great your 8 man team are!", but i think at this state, it's likely never going to happen, because the sad truth is: there are like 400k subs left. Many of those are just casuals who are barely even set foot in an Ops, a big chunk is the PvP community and the VAST MAJORITY are 8 man Guilds. BW is likely never going to encourage ppl to run 16 man, because on most servers it's almost impossible to get 16 decent ppl who are even willing to do 16 man... Again this is my opinion.
And just to reinforce my logic (I DO NOT INTEND TO GENERATE FURTHER FLAME SO PLS REMAIN CALM.):
Gabe Amatangelo: "It is intended that 16 player mode is slightly easier than 8 player mode due to the fact that getting and coordinating 16 players is a larger hurdle in and of itself."
So by default design they aren't encouraging ppl to run 16 man...