Business standpoint says "make it it's own PPV". But this isn't about business, we're fans and you want our opinions.
My vote says to bring it back to Wrestlemania. To sound like an Attitude Era curmudgeon back in my day Wrestlemania felt special. Maybe I was just new to the "sport" at the time but at Wrestlemania 24 and 25 it was this big "showcase of the immortals" in large part because of the massive variety it had. You had Money in the Bank, celebrity involvement, interesting gimmick matches, hot feuds, the Streak, and then some usually well-built title matches. Last few years it's just been "match, match, match, concert, match, streak match, gimmick match, main event". It really feels like a regular PPV again, and think adding Money in the Bank to it would certainly make it feel special yet again.
But you know I'm not going to make a long post without ranting about Creative so here you go: If you put Money in the Bank back in Wrestlemania, that'll make Wrestlemania great again... but it'll probably destroy our interest in the July PPV, lord knows we'll need a great show to get us back interested after the annual creative lull passes and the usual creative lull re-starts. We don't need a regular PPV since they can't make one interesting, so keeping Money in the Bank there is probably for the best.
Money in the Bank as a stand-alone PPV always delivers. Remember last year the card last year looked downright horrific and the PPV delivered in a BIG way. A chaotic match with a bunch of high-flyers that ends with 2 new stars possibly being created every year (and there's still optimism, right Bryan?) obviously makes me really excited as a fan... yeah, think I'll change my vote to keeping it as it's own PPV.