I agree that we dont have useful major glyphs now...at least we lack one more along with FB and FC but Thorns?! You say yourself: "you will want to help out with thorns on tanks from time to time" meaning you cant do it all the time and we all know due to techicality of boss encounters you cant do it all the time anyway. So to apply Thorns you need to go out of the form and apply Thorns and go back to the form. That is 3 second wasted GCD for meager dmg Thorns does. You would probably do more dmg by white hits only in that time. And if you really wanna do it "sometimes" you dont really need a glyph that reduces your Thorns for 20 seconds....unless you want to spam it. In a long run I dont see how is that viable dps increase over not shapeshifting. FC glyph can be useful tho like on Princes, Marrowgar, Deathwhisper, etc....if we are talking about ICC f.e.