0.1 sat/byte fee would be interesting too to see what happens,that's about 20 sats for a standard transaction then. It would be nice to see low fees again soon though.
Currently, Bitcoin Core does not allow users to relay transactions with fee lower than 1 sat/b. Fortunately, this is going to change in the next release of Bitcoin Core (0.18.0).
Here you can find more information.
Does rbf require your input to be used with a smaller output?
There should be the same inputs and outputs with no change to the amount of coins sent + a new input which will be spent on the increased fee and an extra output if there are any coins left from the new input. However,
there are different variants of RBF.