Motta has the experience of the very top level (as a player)… Definitely one of the good candidates out there.
Plus, like Xabi Alonso, he is his own man but has played under lots of different types of coaches (van Gaal, Rijkaard, Gasperini, Mourinho, Prandelli, Ranieri, Ancelotti, Conte, Blanc) and takes inspiration from lots of different tacticians (Guardiola, Bielsa, Löw). That breadth of experience and theoretical knowledge should hold him in good stead as he puts his own twist on things — a few of them were great defensive strategists, some adhered to positional football regiments, others encouraged a bit of relationism, there was considerable variance wrt. in-possession and out-of-possession approaches (as well as a sense of reactiveness and proactiveness), a couple were masters of man-management, and so forth. For example, he recently seems to be doing what Guardiola (and Arteta with White and Kiwior) does in terms of playing multifunctional defenders at the fullback position, that can't be entirely coincidental.
Over the last decade, teams have finished in the Serie A Top 4 with 65, 64, 67, 72, 72, 69, 78, 78, 70 and 70 points. Right now Bologna sit on 57 points, with 8 matches to play. A total of 70+ points doesn't seem unrealistic, and is at least on par with historical norms. Dunno if this is an opportune moment for him to move, though. In an ideal world he would continue at Bologna for a while, further develop the project and at least go through the rigors of playing continental football. Then again, there are no universal rules for success. Someone like Marcello Lippi had zero trophies to his name and had qualified for European competitions for the first time at Napoli when he was offered the Juventus job (traditionally the most prestigious in Italian football). Antonio Conte's résumé was also not the most comprehensive, yet, like Lippi in the 1990s, he managed to define an era with Juventus. Sometimes you need to trust your own abilities and take a leap of faith.
Regarding the Manchester United job, it's fraught with peril. The Premier League has been the most competitive league in club football for a few years. Manchester City and Arsenal are well run from an organizational standpoint and will continue to dominate the top end, in all likelihood. There's no assurance that United's structure will be sound and resilient enough to adequately support a fledgeling coach. Never say never, but it might be too much too soon for Motta.