I've being given things some thought as what my Professions will be come WotLK. I'm not much into changing Professions. I've had the same professions since starting the game. I play my professions more for fun and what I enjoy more so than whats best for me as a spec as both have served me absolutely well for fun and pure economics. And I like economics.
I enjoy Herbalism and Alchemy. Its also funny because I work in the Pharmaceutical Industry in real life which almost somewhat relates to Alchemy. But I enjoy my professions as fun as well as playing and manipulating the AH market in that mini game as well I like to play. I'm not worried one bit with Alchemy in WotLK whether it has BoE stuff or not. I like playing with Potions and Elixirs so Alchemy is here to stay. One thing is I know how to make money with Alchemy so i'm not worried.
When it comes to gathering Profession and Herbalism I'm less sure if I will keep it. There is nothing that interesting with Herbalism. I enjoy it but with WotLK my own perception tells me that mining is a winner and would be good to take up especially with all the crafted gear needing Saronite and Titanium. In Beta you can barely find Titanium anywhere to craft Epic pieces. Alchemist can also transmute Titanium with metals from mining as well so a bonus. But switching Herbalism to Mining would not be that hard as my Paladin have max Herbalism and my lvl 70 Hunter has max Mining.
All that would need drop Herbalism for Mining on my Paladin and have my Hunter drop mining for Herbalism. Fair trade especially since I'll level up my Hunter 2nd after my Paladin so I'll still have ability to get Herbs for my crafting. But overall I think picking up Mining would be a better bet in WotLK than having Herbalism on my main character. At least I will have Herbalism on my Hunter to still support Alchemy.