The above image was taken in tricky light. However processing the raw file in Photoshop has produced a balanced image with good dynamic range, low noise and satisfactory sharpness. The file is sitting on a stock library website. And below is the size information for the image. As you can see it's 34MP.
So how was it created? Well it's a image shot on a Microsoft 950X smartphone, run through Iridient Developer and Photoshop and upsized (interpolated) 135%. And if you read some parts of the photographic internet, what I've done is a mortal sin and if you read other parts, what I've done is incomprehensible. I've made my file size bigger than when it was shot on the camera. But anyone who was a stock photographer in the period between 2001 > 2005 would have been doing this all the time. And digitally shot images on any decent camera / lens / sensor combination are perfectly capable of being printed at double their original size.
So why don't more people do it? To be honest I don't really know. Perhaps it's something to do with the kind of 'advice' that comes from the photographic internet. A lot of sites depend financially on people upgrading and buying new cameras. So making out that m4/3 'upgrading' their sensors to 20MP from 16MP is a big deal is in their interest. In fact it's no big deal at all. A classic example of this is the Leica T (Typ 601). I saw some comments that the new upgraded TL was flawed because it used an 'old' 16MP sensor. Well on my Leica T's I've been upsizing my files to 24MP ever since I bought the cameras. They look fine, helped by the lack of an AA filter and even it they get reproduced at the full size, which is very rare in stock photography, they will look exactly the same as 'genuine' 24MP files at most levels of reproduction.
So maybe when you think you need a camera with more pixels. try upsizing the images from your current camera first. Sure, when 'pixel peeped' at 100% you might see a difference, but then I remember a printer at a repro house telling me ages ago, that if I wanted to see how an image would reproduce in print, then I should view it at 50%, as that was a much better guide as to ho an image would like like after publishing and printing. And of course as soon as you do that, differences between sensor sizes and pixels pretty much disappear.
Finally, I've had 6MP files upsized to 16MP and more sitting (and selling) on stock library websites for years and no one has complained. Simply because there isn't really anything to complain about anyway. As you see from the image at the top of the page, you can even do this with the best of the current smartphones, providing you take care with processing, always use raw files and use the excellent tools for upsizing that many software programmes now have. And if you want to give it a try the excellent Iridient Developer has some really excellent ways to upsize images and you can download it for a free trial. Maybe after seeing what that can do, you might think that you don't want that upgrade after all.