Well, the only thing I'll say is, if it were to become confirmed in the manga, at least no one should have the right to act surprised or claim that it wasn't forshadowed, there are many signs that point towards Minato being a Senju, more specifically, being related to Tobirama.
1) Physical Resemblance - as you mentioned, they do kinda look alike and their haistyles are similar.
2) Talent - both were hailed as jutus creators/inventors, both use FTG as their primary fighting style, both are naturally blessed with speed, both have the same sensor capablities and even related tracking jutsu (finger tracking/sensing jutsu).
3) Personality - both are cold and calculating in battle and they don't hesitate to kill in battle, in fact, it seems like they both like going for the immediate kill.
4) DNA/Genes - Kushina was an Uzumaki, and in fact, she was said to have chakra powerful and special even compared to her kinsmen. Yet Minato's physical traits were able to genetically dominate her own, resulting in Naruto inheriting more of his physical traits than hers, even overwhelming the Uzumaki trademark red hair. This should not be possible unless Minato was from an equally powerful clan, which can only be Senju clan.
5) Kishi made a point to develop a relationship between Tobirama and Minato in the war, they tag teamed together and comparisons were made between them. There's even a part where Tobirama lectures and talks down Minato almost like a parent figure. This could be viewed as forshadowing.
6) Perfect Sage Mode - it has been forshadowed in the manga that you need to be of blood relation to the Otsutsuki clan in order to become a perfect sage, hence only members of this relation (and those who implanted their dna, ie...Madara and Kabuto, Kabuto being with Karin's dna, have managed to become perfect sage), Minato as we saw has the sage eyes that signal that he is a perfect sage, and no other body part of his was transformed. Therefore, he is a perfect sage, but has had enough practise to increase the time limit, and probably didn't get any as he finishes his battles prematurely.
7) Finally, I fully acknowledge that this is pure speculation, as this has not been in anyway confirmed in the managa, but the signs are overwhelmingly in favor of this possibility. In any case, if it is not confirmed in the manga, then it is not fact is the truest sense of the word, but if it does get confirmed, I don't believe anyone should have the right to be surprised or claim asspull with so much forshadowing. Oh and Naruto being Ashura's reincarnation is even more evidence, as in the past only Senju have been Ashura's reincarnation, so why now all of a sudden an Uzumaki? Tobi kept talking about these clashes of fate between Senju and Uchiha, and he said Naruto and Sasuke were next, why Naruto if he is not a Senju? Why does Naruto not have red hair?
