Hell no! And I'm a huge, HUGE fan of BOTH series'.
Fullmetal Alchemist: Brotherhood ended and solidified it's place as the greatest anime of all time! So if there's a sequel - or - anything in that nature, it'd ruin it's name and rep. Mostly because I highly doubt Yasuhiro Irie & Hiroshi Onogi could create something equal to or greater than FMA(B). Why? Because Bro-hood was truly the epitome of perfect. And you simply can't exceed/go beyond/surpass that which defines perfection - can you? No - especially if it's in regards to Fullmetal Alchemist: Brotherhood.
Lastly, if there was a sequel and it wasn't as good as FMA (the first one), than it'd lose all credibility of being the greatest series since the sequel would be apart of Bro-hood. Hence, for the sake of it's title of the best, it should not have a sequel!