I thought that it only makes good sense (especially when used with AUR helpers like cower or when writing/updating an AUR helper) to have an --asdeps option, as in pacman, for makepkg when the -i option is used. Marking packages as dependencies isn't automatic with at least some AUR helpers, and it certainly isn't with ones like cower where the user invokes makepkg on his or her own. Such an option would allow the use of the -i option in all instances instead of having to use makepkg and then pacman either with "-U --asdeps" or "-D --asdeps," depending on whether -i was used.

In short: so long as makepkg is going to have the -i functions, an --asdeps is exactly the sort of thing that should probably be able to be passed along as well.