The asymmetry is inherent to the nature of the arrangement - you promise a trader control of some funds until they choose to release them. Granting lenders any more power to recall their funds would open the potential for traders to be forced onto more expensive swaps than they'd agreed to.
Correct. I'd not give lenders the chance to close it early, that would wreak havok.
In general though the problem you're trying to solve (that traders will take out a swap for long periods then return it sooner) isn't really a problem - traders already pay a premium for 30 day swaps because there are fewer of them available and they normally start at higher rates than 2 day swaps.
True in theory, usually not in reality though. But you're right, that argument is compelling enough not to change anything. It the lenders' fault that they dont ask higher premiums for longer durations.
Edit:
@DebitMe
Well, main focus of bitfinex is to make trading for traders affordable and convenient. Creating a lending-syndicate isnt in their best interest. Plus implementing THAT is potentially a lot more complex than the easy calculation I suggested. Even if they did want to do this, they'd need to assign some manpower to this without much benefit for finex.