The outer voices would move into a P8 by leap which is supposed to be hidden octaves and not good. Is this indeed a bad progression and would another harmony be better here? I normally would just stay on I here but if I have a weak beat ^3 followed by a strong beat ^5 I wont be able to use the same chord.
If you think of the outer voices especially in terms of two part writing, then the bare octave also becomes a bit of a concern. It sounds sort of "hollow."
The way out of that is a preference for thirds/sixths:
^3 ^5 harmonized with
I V6. I think this would be the "standard" two part harmony for
^3 ^5 and tonic/dominant harmony.
Another way to think of the implied harmony of
^3 ^5 is simply an arpeggiation of
I, and so no chord change.
I supposed you could mitigate the direct octaves concern by moving the base in contrary motion.