The vast majority of the content I care about in a homebrew setting is invulnerable to edition (or even system) changes. Every edition change brings with it new ideas that I use, or a better way of doing a certain something; minor details might change but that sort of change could easily enough happen with me seeing a cool movie, reading a novel or comic, or just being struck with a neat new idea for the setting. Just because, say, 4E might not contain Frost Giants right out of the gate just for example, doesn't mean suddenly Frost Giants will disappear from my homebrew or that I won't use them in some capacity.