I don't think they can get Nagelsmann otherwise Bayern would've snagged him already but going for Arteta is a huge risk given that the club is already in decline. Now isn't really the time to be taking risks with hiring managers with no experience. People can point to Nageslmann being a risk but he's taking his small and unfancied team to two consecutive top 4 positions, which is a massive acheivement; certainly a much smaller risk than Arteta.
Arsenal have to break the bank to bring in someone like Allegri, Jardim etc. Someone with experience who can steady their falling ship, signing Arteta, for whom no one has any idea how he'l manage a team, can send the club into mid-table mediocrity if it turns out he is out of his depth.