This contract is less about Arteta or Edu than Nelson himself, I think. Retaining Nelson as a second string forward when he's being courted by other serious clubs is a financial no-brainer.
What's good about this is it seems Nelson's staying on out of loyalty to Arsenal and a personal ambition to succeed at Arsenal—two things a lot of young players who've gone through it like him wouldn't have.
I really like the situation as he has everything to prove but he'll know he has to. He's entering his prime, there are some hints his attitude is more serious, and he may well find another level.