Xavi could be a good choice if he'll get time. Barcelona are a shambles at the moment so it's going to be a very tough job. Be surprised if he brings any kind of instant success. Their goal for the season is pretty much only making top 4 and building for the future. Can't do more than that.
With hindsight, Koeman must regret accepting the job. Having Messi and Griezmann go, all the financial and other problems. Hasn't done himself any favours and pretty much any manager would have struggled given what's gone on.
It can go quite wrong for an inexperienced coach, so it's also a risk for Xavi taking the job. I think Pep will go back in a few years, now Bartomeu is out no barrier to it.