The resolution wars

Digital cameras are not high enough resolution yet. What, I hear you cry, you can buy 12MP for under a grand now. Well, yes, you can. But that's not enough. The problem is that this particular game is set up for standard sized photographs. 5 inches by 7, say, or perhaps a little larger. Big in this context is A4 sized. And that's fair enough. But I want to put my pictures on the wall, so 20 inches by 30 is a minimum. A decent printer gives 360 dots per inch, but let's be charitable and call it 200. Then 20 inches is 4000 pixels and 30 is 6000 so 20 x 30 is 24MP. And remember that's a minimum. Ideally I'd like to be able to crop that image a little, and print it larger. So really 50MP is a sensible resolution to aim for. It might be a while before I buy a digital camera...