At the shows in New York, Mikael assured us that it isn't the end of the death growls. He actually let out a death grunt and said to the crowd "don't worry don't worry...we're just trying something new for a little a bit, that's all"
Even in that interview (if you actually read past the headline), Mikael says: "I've never turned my back on anything and I'm not going to start now. It's not like I don't like that style of vocal delivery anymore...if the future songs require those vocals, then that's what I'll deliver." And I'm guessing what he means by "not being able to develop that style of singing anymore" is that he's perfected it and that's it, he's taken it as far as it can go but he's getting better as a singer and wants to develop that style fully. He still LIKES growling.
Mikael is writing music and growling is just one weapon in his arsenal...it doesn't mean he has to use it all the time.