My two daughters are both music ed. majors (strings), as was myself and my husband. If he wants to be a band director, he will most likely be in the “band track” in his degree program. Music ed. majors usually follow one of three tracks (vocal/general music, band, and string) each of which prepares the students a bit differently, getting them ready to teach within their specialty, though of course there are many of the same classes they all take. I don’t think taking another wind instrument will necessarily help in admissions - that will mostly be based on his percussion audition, his grades, etc… It WILL help however, in his band instrument proficiencies that he will have to pass. The students in the band track are expected to have a higher level of proficiency on all the woodwind, brass, and percussion instruments than a vocal or string music ed. major. The students in those tracks do have to pass proficiencies on the band instruments, but at a somewhat lower level than the band track kids. Of course the string kids have to pass higher-level proficiencies on the other string instruments than the band and vocal kids, while the vocal kids usually have higher-level proficiencies to pass on piano, etc… So your son will have to pass an easier-level proficiency on a string instrument, but as he’s been playing one already for all these years, it will be a piece of cake for him. So, investing the time getting familiar with a wind instrument now will definitely help him out later on. I think he should go for it if he’s interested. Good luck to him!