My experience with all sorts of things is to stick to the standard aspect ratio. When 5:4 (1280x1024) became popular, it was a problem. When 16:10 gained traction, it was a problem.
Some games (only a few) will barf at a weird resolution, but most of them will run fine. However, even if they do run fine, there are constantly problems related to overdraw and clipping. Multiplayer games sometimes clip rather than extend your view to avoid an unfair advantage. Other times a sloppy port from console titles means that HUD or offscreen elements don't draw as expected. In general the big AAA titles are good but the really cool stuff is the indie scene and these guys don't often have the resources to fine tune their products for weird niche products.
Most TV shows are recorded and optimised for 16:9. If you're a big movie fan, the 21:9 will help, but you're usually better off using an HDTV anyway (sofa > chair and, uh, it's 50" and not 29" so the picture is better even when you're letterboxing).
For what it's worth, 27" QHD is gorgeous.
Some people ask me why I have always enclosed my signature in spoiler tags; There is a good reason for that, but I can't elaborate without giving away the plot twist.