there has to be some other reason they're pushing for this law (perhaps just general harassment of gun owners?).
The underlying motivation is to make it difficult for firearm manufacturers to comply with differing laws all over the place. They need to make one model gun for California, one for New York, one for Massachusetts, and so on... Eventually those makers will just decide to stop selling in that state. This will likely trigger a spike in the price of firearms, so that only the wealthy can afford firearms. This is the intent, but likely all it will do is expand the scope of illegal gun trading in the state, congrats california! Swap one problem for a much worse problem, a bigger black market for firearms.
Where does it say "the right to bear arms in a way that can't be traced"?
The constitution doesn't say a lot of things, that does not mean that there is free reign to do such things.
If they could use a controller, absolutely. But multi-touch gaming is just not convenient. A few games can pull it off and last the test of time, but nothing that's in the market that GameStop caters to. The controller is a MUST and it may make the machine a killer device, a portable console that doesn't suck.