Preloading is a primitive operation. You must preload for a year or more, and "be aware that inclusion in the preload list cannot easily be undone," according to the registration tool. Therefore, if there is ANY chance of an error, it is prudent NOT to preload, at least for awhile. During that time your website is wide open for MiTM attacks by each first request by each visitor (to find the HSTS header).
Is there any simpler solution, one that doesn't have the problems with redirection, http access, and preloading?