I had a dream about some random combat (not cs related) but when I woke up a cool cs mod came to mind. Don't really know what you would name it but heres the idea.
When a person walks they are 25% visible, when they run they are 50-75% visible, when they dont move they are 0% visible. But if they get hit, they become visible completely visible for a second. The same applies to firing, except if you wanted to get real creative you could make it based on which gun they were using. Like a silenced gun would only make them 50% visible, and the biggest ones like an awp 100%
It would be kind of neat playing under these conditions, worth trying.