This is a tough one. My son worked with a track coach who at one point in time was an Olympic sprinter. He worked with him just to get some help in technique and my son got to know some of the kids who were sprinters that this coach was training. What struck him (and me) watching them was how much work has to go into being an elite runner. Weight room, field work and technique work, the top kids had very full schedules being sprinters. A couple of the kids he worked out with went on to run in college.
I guess it boils down to where your son wants to take his gifts. The scheduling issues alone probably would prevent dual participation as HS track meets are typically a long affairs, as are baseball games, forgetting about the training issues. During my son's HS years I am aware of one athlete who participated in basketball and soc cer, who were both in the same season. The coaches worked out the details, but basketball games and soccer games were generally on a different schedule with basketball typically later in the evening during the week. In his case soc cer was his primary sport and he back filled with basketball. He went on to play soc cer in college.
I guess it comes down to whether your son could compete at the higher levels of sprinting without putting in the same amount of work as his competitors and whether the coaches would work with each other. One sport would have to take a back seat to the other. The other issue, as you pointed out is the sheer amount of time required to do both and continue to keep his grades up.
Good luck to your son.