Note that bitswap isn't purely a tit-for-tat system, but will also include a credit system like you suggest.
> I have designed a protocol that allows nodes to transfer credit to cancel out 'cycles of debt'.
Awesome, sounds like if Filecoin were based on Ripple instead of Bitcoin. Ideas are always welcome, so please share yours either via Github issues or IRC (freenode#ipfs) :)
It's fundamentally different than Ripple. From wikipedia:
Ripple relies on a common shared ledger, which is a distributed database storing information about all Ripple accounts. The network is "managed by a network of independent validating servers that constantly compare their transaction records."
I don't think any system that relies on a global ledger is workable for micropayments like this.
Edit: I spoke too soon, Ripple is more complicated than I thought. It is somewhat like Ripple.
> I have designed a protocol that allows nodes to transfer credit to cancel out 'cycles of debt'.
Awesome, sounds like if Filecoin were based on Ripple instead of Bitcoin. Ideas are always welcome, so please share yours either via Github issues or IRC (freenode#ipfs) :)