Toneri could not awaken the rinnegan, so even if he took interest in the Uchiha, he'd be limited to MS at most (which is strong, but not enough to destroy the planet, which is what he was trying to do). Byakugan and its evolutions are naturally compatible with Toneri and the other moon Otsutsuki descendants of Hamura (as that is what they were born with, they simply gave up their eyes to the tenseigan altar). This is not the case with sharingan.
Sure, he could try to take Sasuke's eyes, but he'd fail miserably (especially if it was eye-less Toneri vs Sasuke).
Sarada wasn't born at the time, and who knows if the Shins were born (and if so, how would Toneri know about them)? If he was lucky, maybe he could find Madara's corpse and take his rinnegan, but even then he wouldn't be much better than Nagato.
Basically, if he were to focus on the Uchiha (assuming that the time period was still the same as The Last) then Toneri would be limited to finding a dead Uchiha's sharingan eyes and hoping that they were at least MS level.
