Flashloans are a fascinating economic coordination mechanism that has emerged out the Ethereum architecture as a result of a synchronous, sequential, atomic transaction system. It allows anonymous coordination between capital providers and arbitrageurs because the capital providers can condition providing any capital on protocol enforced guarantee that the entire arbitrage is profitable denominated in the token being lent.
One of the effects of this process has been the it ensures an efficient and healthy liquidation market for the collateral in long term debt instruments. It also enables low cost scaling of economic exploits.
Flash loans are impossible in an IBC world because IBC semantics require finalizing a block on the origin chain rather than on the receiving chain. This makes atomicity for the lender difficult and moves us into the domain of over collateralized lending.