The chances are pretty high that there will be a bunch of weapons and gadgets in the game that will now never be used by anyone.
That might not be a bad thing. If players don't like them or find them useful, they shouldn't be forced to use them, IMO. In the past, with weapons locked to classes, you sometimes had to use a poor weapon to get an ability that you wanted or take an ability that you didn't want to get the weapon that you wanted. For example, in Battlefield 2142, few people played Engineer because the rifle choices were poor, despite the Engineer's other weapons and tools being highly useful. The latter ended up not being used much because few people (me included) wanted to put up with the Engineer's rifles, which basically created the problem that you described. On the flip side, I imagine that some players might consistently pick certain classes specifically because they like the rifle and have no interest in using the other tools and abilities of that class. For example, a person might like the Medic's rifle, but have no interest in healing. If he could pick that rifle and choose a gadget that's more to to his liking to go with it (like C4), he might actually use that gadget and help out the team more than he would've as a Medic who refused to heal. Either way, there's the possibility that the most useful abilities and gadgets could actually increase in usage if players aren't locked into specific weapon choices (and if the less useful ones decrease in usage, that doesn't seem like much of a loss).