Will Iota adopt brain wallet similar to Nxt?
Yes. But the seed will be forced to 81 latin letters and '9'. Nothing stops other devs from using another approach, of course.
Exact 81 characters for a brain wallet seed, so it seems a little inconvenient for the user memory and input. I think there will be definitely some other wallets available with great random entropy and easy for use, say wallet file similar to Bitcoin.