Personally, I don't really care one way or the other. I have all 9 crafters, and I don't sell much from any of those classes anyway other than adornments.
The real issue is the imbalance between the tradeskill classes regarding consumable items and usefulness. Provisioners make food/drink which everyone needs and there is a constant demand. Weaponsmiths and Armorsmiths make items that are inferior to dropped and with no decay the demand is light.
Personally I liked the item decay that Star Wars Galaxies had. It ensured there was a constant demand for all tradeskilled products because everything was consumable. Now, SWG also had a crafting system with individuality and uniqueness that was far superior to EQ2's (IMO), which also allowed the best tradeskillers to make items that were truly better than the competition. I do actually lke the concept of dropped items allowing WS/AS to craft superior items.
I think joining classes would be a bandaid, no a tiny bandaid, to fixing the bigger issues outlined above.
One additional thought: what about crafted armor sets with bonuses for 3, 5, or 7 items equipped?