I have an ancient Epson 7600 24" printer downstairs that prints 24" by however long a print I care to make, and I love to make big prints. A 24x36" print from my 5Dii gives roughly 160 pixels per inch on the print. A 6000x9000 54MP sensor would give me 250 dpi on the print, and I have many lenses that can make use of that resolution because they show great detail on my wife's NEX crop body, and on that size print, the difference will be CLEARLY visible. Even the 16x24" prints I make most often will look better, viewed in the hand as they often are.
Now, there are people who will soon chime in and say that if my 24x36" print from a 5Dii doesn't look good, it is my poor post processing skills, or I'm viewing too close. To the first point, if the detail isn't in the capture, it won't be in the print, and to the second, well I'll look at my prints any way I want to, and you may too as far as I'm concerned. I want them to look like I want them to look. I want pine needles to look like pine needles, dammit, even in a shot that is not OF pine needles. That's what they look like, not blobs at the end of detailless branches.
Having said that, I think that if you take pictures of people, which move, or shoot hand held without a flash in less than direct full sunlight, there is likely not a lot of point in a 50MP camera. Pictures of relatively large objects filling the frame relatively full have plenty of resolution now. Pictures of hot air balloons can be printed any size from any camera. Portraits at 22MP have more detail than most people would want to see. But even having trees look like actual trees do in a wide angle shot is a whole lot tougher.
I know...just shoot panos...
Frankly, 50MP is just a step in the right direction for some of us. I'm pretty sure even my $280 Sigma 70mm macro would hold up fine on 100MP. Not sure about my tripod technique, though.