A better way to train future Theoretical Computer Science researchers
One downside is the "all eggs in one basket" problem. If you're sure you want to go into theoryCS, then this is great. But if you want to hedge your bets, then some more programming and general CS courses at the undergrad level would be helpful. Also, even within theoryCS, a solid understanding of computer science at large helps with asking new questions about other models of computation, or evaluating the value of theoretical questions motivated by some practical applications.