If there is interest, it will create more "claims" on bitcoins than there are bitcoins that exist. This is deterministically true and the simple math is above to illustrate it.
So, we have two things:
1) Bitcoins (created through mining)
2) Claims on bitcoins (created through usury)
The two are NOT the same.
So, at some point in the (distant?) future, we will have a situation where there are 21 million bitcoins, and claims against 210 million bitcoins.
That is, when people suddenly start calling in claims on bitcoins, the debt system begins to rapidly unwind, as in a "run on the 'system'". That system MUST be outside of the bitcoin system though because it's not a part of the protocol, i.e. that's trivially true.
THE QUESTION REFRAMED FROM THE ABOVE:
Is this problematic that there will be more claims on bitcoins than there will be bitcoins in existence?
My gut reaction is that usury, with respect to bitcoin, it nothing more than counterfeiting fake bitcoins and convincing people that they are real, which we know is false, i.e. a claim on a thing is not the thing. The implication then is that usury will create inflation for a currency that is inherently deflationary (if nobody objects to framing the terminology like that).
Not quite. In my original post I thought I was pretty clear that I wanted to frame the question in 'frictionless universe'. The question isn't about practicality, it's theoretical.
I understand the velocity of money and how that affects systems, but I think you might have missed the point above where I glossed over the velocity and assumed a near infinite velocity (zero friction).
Since the system is deterministic, it's only a matter of time before claims on bitcoins eclipse the number of bitcoins in existence. Any talk about the velocity of money is just arguing about "when" the claims eclipse the real thing. I am not worried about "when". I'm interested in the implications of that eclipse.
Right now we have central banks printing fiat money out of thin air, and it seems to me that usury is not significantly different. I'm merely framing that issue in terms of how usury is compatible with bitcoin as bitcoin has a hard limit on the amount that can exist.
Another way to look at it is how JP Morgan, Goldman Sachs, and now the Fed have been shorting silver and gold - paper silver & gold. By manufacturing imaginary silver & gold, they've managed to manipulate the market and crash the prices.
In terms of bitcoin, the imaginary bitcoins (claims on bitcoins) created through usury seem to lead to the same problem.
I just don't see how usury is compatible with bitcoin unless we want to go down that same road that we see with other fiat currencies and paper silver/gold.