Open Source in this case might not make much of a difference. If this is written in Swift and only runs under iOS, or if it ties with a certain Apple service th

Open Source in this case might not make much of a difference. If this is written in Swift and only runs under iOS, or if it ties with a certain Apple service that requires certificates issued by Apple it won't make much of a difference if you can read the full source code, even if it's released under an MIT or similarly open license. As long as the data this gathers can't be used (or contributed to) by a third party, it's still a 100% Apple property, regardless of code availability.