You are more likely to run into text being to large in that scenario. I have Ultrawide 40" 5k2k & 32" 4k computer monitor and run linux with Steam. Text is fine, It is just going to get larger on a bigger screen. Steam has scaling for its interface and Plasma, the desktop for SteamOS, is feature rich for most people's usages. I am certain people already are using Linux and Steam with TVs. If there is an issue, it would also be an issue on Windows. Mostly older games that weren't updated for HiDPI screens.