Feel like 1520 can handle four column live tiles.
Well that'd be interesting, but we don't have the option, unless say, the model was jailbroken, which hasn't happened for any WP 8.0+ Lumia.
Probably but they are losing sales from not allowing fewer (two) columns. I know someone with a 925 who passed on a 1520 because the three column live tiles are SMALLER and harder for them to read than the 2 columns on the 925! I think MS may have overlooked the elderly or otherwise vision challenged audience who would buy a phablet just for easier reading if only it allowed that to happen via two columns. Once you open an app, things are bigger but they want the same for the live tiles.
I wonder how the Windows 10 will present live tiles; and if it will allow for screen rotation. Seems that live tile sizing should be a simple function for an OS. Some websites use responsive masonry tiling these day, too.