Tomlin/Harbaugh candidates for Texas?

Texas Longhorns coach Mack Brown is expected to resign by the end of the week, leaving an opening in one of the most coveted jobs in all of college football. Texas will presumably draw with high leverage on candidates from both the college and the pro ranks and the administration will likely try to bring in someone who has championship experience. A report from Chip Brown of Orangebloods.com alludes to Pittsburgh Steelers head coach Mike Tomlin and San Francisco 49ers head coach Jim Harbaugh as possible candidates. Is either option realistic?