Under the new format of UEFA champions league and europa league, no team from the champions league will qualify for the europa league and all teams that won't advance to the round of 16 will be eliminated.
You're right. With the new format, there will be no teams from UCL to play in Europa League when they are eliminated in group stages. I think it will be fair, all the teams in UCL will focus on the UCL matches only since the early of the competition and the teams in Europa League won't be afraid because of the possibility of some teams from UCL after the group stage.
I don't consider Sevilla winning Europa league next season but it is possible if they are in form because we all know that they have the experience more than most of the countries playing in this league next season.
Even if Sevilla could win Europa league trophy several times in the past, they have no longer strong squad recently. Moreover, Sevilla isn't qualified for Europa league competition, right? How Sevilla can win Europa league trophy in the next season? As far as I know, Sevilla only could finish in the 14th place last season. 2 teams joining Europa league from La Liga are Athletic Club and Real Sociedad.