I don't really see the use case you're looking for here

Exactly. Leaving 0 reserve has negative impact on your channel partner, but spending and closing doesn't.

BallLightning

then question becomes "can we re-negotiate the reserve to 0 along with the preimage of spending the local balance"?

in this case it would need to happen simultaneously somehow.

lightning

Spend all in channel and close

then question becomes "can we re-negotiate the reserve to 0 along with the preimage of spending the local balance"? 
in this case it would need to happen simultaneously somehow.