It is hard not because of UI (whether it is a button or hotkey) but because of how it would interplay with other things in the code, in this case such as the tone mapping. As I say, what looks easy from the outside may not be so easy once you are inside the code :) "Wait, how does this interfere with the tone mapping code?" you ask - well that's what I mean, unless you are a dev with access to the code, such things may not be obvious. BTW nothing here is about it not being important, but about it being "more complicated and time consuming to do than you are assuming" - which is why we have it logged for future work, as we understand people would find it useful.