You are again misconstruing what is being said. I7 is not traditionally tonic. Please correct this notion. In American based music, I7 can be considered tonic, but it's actual function is dominant. (blues, jazz, pop and country) Any tritone is a dominant function. Tonic is a repose function. Writing out triads long enough, everything becomes dominant, but very muddy and ambiguous (like this particular sentence). New rules apply.

An Asus4 is an implied dominant chord. If you want to use it as a I chord or IV, fine, go ahead. (the tune sounds like it doesn't end, not a bad notion, as IV delaying resolution.) The natural resolution is 4th to 3rd. Not all tunes end on I,i-vii. Don't make this more complicated. Dominant or dominant types, or function, move the music (almost every type or genre). Dominants can conceiveably go anywhere. It's because of the nature of the tritone. Dissonance.