If he rejected Al Nassr, he probably rejected Al-Ettifaq as well. Al-Ettifaq isn't a bigger team than Al Nassr, they also have no star players like Ronaldo or Mane. So, De Gea has no reason to join Al-Ettifaq. If De Gea wants to move to SPL, I'm sure he will choose Al Hilal, Al Nassr, Al Ahli, or Al Ittihad. If there is no offer from these teams, I doubt he will come to SPL next season.
No way for Al-Ettifaq to send De Gea a better offer than what Al Nassr can do. De Gea will consider both issues, salary and chance to win titles and if both Al Nassr and Al-Ettifaq send him offers, if he decides to move to Saudi Professional League, Al Nassr will be his choice because they are able to make better offer than Al-Ettifaq and can give De Gea more chances to lift titles.
You're right, there are no many rumors about the interest of top European team to negotiate with De Gea. But it doesn't mean there is no European teams that has the interest to sign him. I'm sure there will be European teams trying to negotiate with him, specifically the teams in La Liga or EPL. Just wait for the time when De Gea decides to join an European team.
It is something I feel weird as De Gea is a goalkeeper who can provide very good quality for any club. Likely problems are from De Gea, like he does not want to play in some leagues he does not like. If he opens to all leagues, he will receive many offers from big to small.
At his age, playing for clubs in La Liga looks to be best choices because he and his family will have chance to live at their home land.