I think Solo would've been drafted if he left this year, and I think he'll be drafted whenever he decides to leave. How high will be determined by his development in his areas of weakness, but he's easy to project as a role player.
Elite shooting is still a rare and needed skill, and Solo is in the upper percentile of shooters on the planet. He'll be a good fit on a team that uses a larger point forward type to mitigate the size issue.
But also remember Solo is jacked, he's functionally bigger than Mullins right now, even if Mullins has an inch on him.