I'm not sure I follow you Aiki. Are you asking if you get something special for unlocking achievements (outside of the warm fuzzy in the cockles of your heart), or are you asking if the updates to TF2 will include achievements that you must obtain in order to get new weapons?
If you're asking the second, then yes. In order to get the new weapons (like the medic's overhealer), you'll need to get around half (35 or so, as I understand) of his unique achievements. Multiply that by nine classes, and you've got around 630 possible achievements.
Of course, that's all theoretical, but that's my understanding of it now.