I could be wrong about this, but I seem to remember hearing a few years ago that Roush was the only major team owner that has been around a long time without a clear line of succession in place. It's not surprising that he's searching for someone to follow in his footsteps. Keselowski wouldn't be a bad choice at all.
When Tony Stewart took an ownership role at Haas, the organization had been in Cup for 6 years with no finishes better than 5th and a season-best point ranking of 28th. In their very first season together, Stewart won 4 races and both drivers finished in the top 10 in points. Solely based on stats, Keselowski would be entering into a much better situation than that, though it's hard to know what it would be like behind the scenes.
There is also a lot of irony in this for Ryan Newman, who left Penske to join Stewart at SHR but could now potentially lose his ride if Keselowski leaves Penske to take this ownership role at Roush. Then again, with the new car coming in 2022, Newman could be thinking about retirement anyway.