What would Walt think of this movie?
I think he would like it, approving of its deep portrayal of Goofy and Max.
I don't see him having any discomfort about Goofy siring a kid. He allowed the creation of Junior in the George Geef shorts, not to mention Pluto Junior and Pete Junior in the 40s. In fact, I think he might actually like Max, seeing him as more fully dimensional then Junior. However, Walt might disapprove of Goofy being too soft on Max, wishing the kid get some punishment for his attitude (Walt once hit his daughter for disobedience. He felt bad about it but admitted that the kid deserved it).
Of the mature content...Walt would allow Max's 'wet-dream' (he allowed Ichabod to dream about marrying Vanessa for her money in THE ADVENTURES OF ICHABOD AND MR. TOAD), though he'd wish Max wore some bedclothes. He probably wouldn't like the scantily clad Powerline-ettes (nor have Max be fixated by them) or the diva singer Goofy accidentally walked into. He'd prefer they be dressed more cladly (Not that Walt was some frump. In MELODY TIME he allowed Pecos Bill's gun to go off when he spotted a hot chick, and the 'love bed scene' in LADY AND THE TRAMP). He might think Stacey would be a better match for Max than Roxanne, in the nerdy underdog plot cliche.
Walt would also wish a more cohesive story. He would require closure to the Bigfoot and Pete plotlines. Perhaps he might want some mention of Max's mother. This could be a sensitive issue for Walt. Goofy divorced would be out of the question in his period mind-set, but Mrs. Goofy being deceased by childbirth might be too personal a discomfort for him (In 1938, Walt bought his parents a home. But the place had a bad furnace with gas leaks that fatally asphyxiated his mother. This...goof-up haunted Walt for the rest of his life). Then again, this is the guy who took some liberties in adapting BAMBI but decided to keep that nasty business with Mrs. Bambi...