At this point in the game, I think it would be a bad move. It certainly would have people who'd leveled up those classes previously stepping all over each other's toes.
Weaponsmithing in particular would benifit from such a change in some ways, the other classes not really other than gaining some extra recipes. Carpentry does fine on it's on. Armorer does just fine on it's on. Woodworking, has some flaws, but also does fine on it's on due to it not being solely based on the weapons it creates. Weaponsmithing does fine up until the mid 30s when players get zones like Runnyeye which drop so legendary quality weapons that it becomes easy to ignore the smithed ones, especially after adornments were introduced. In the tiers following it varies depending which zones the player plays in but Weaponsmithing is horrible in Tier 7 where everything and it's grandmother seems to drop awesome legendary weapons. The new changes to allow imbued weapons to be adorned should help a bit, but the base damage of all playermade weapons serious needs to be looked at or no matter what changes you make, player made weapons will always be looked on as secondrate.
Then there are the people like me who have one of everything. We'd suddenly end up with 2 of 2 different classes which isn't nearly as appealing as it might sound to some. There is no way to replace or reimburse people for all the money and time put into leveling all 4 of the classes that could potentially be affected.
Before ever considering such a drastic change, I suggest looking at exactly why some of the classes seem to need help. I think you would find that after looking at that, you'd see that it isn't really the number of recipes that is the problem with the classes more an issue of the quality of the items produced.