I don't understand your complaint. Carcharodons exist at the same time as the Raven Guard, just later in the Raven Guard's history.
well there is the Hunt for Volderius battle novel, as well as Savage scars. Both of which are good. But i also figured they'd be popular because there one of the more popular armies in my area, after the imperial fists of coarse.
Personally I've never seen a White Scars army. I've read the Hunt for Voldorius (which also features the Raven Guard) but haven't picked up Savage Scars. They don't have a popular series which people can grow attached to. I'd like more White Scars books simply because they are all but ignored.
I remember back when the Third War for Armageddon released the Salamander's army list (if you could really call it an army list) and nobody played them. Then the, in my opinion, great Tome of Fire trilogy was released. Now I see Salamanders everywhere. Hopefully the White Scars will get their own series to push up their popularity.
Personally I'd like to see a more obscure Chapter, namely the Carcharodons, only because they're my favourite.
Imperial Fists, because they balance out the chapters nicely. You have two focused on assault (Blood Angels/Space Wolves) One balanced (Ultramarines) And two focused on shooting (Dark Angels/Imperial Fists) Edit: Also, because I'd only make a space marine if he could be an Imperial Fist.