ETH => Secret bridge. What's the business model?

Usually the APY for staking assets comes from trading fees of an exchange ( e.g. Synthetix pays you the APY from Synthetix.Exchange fees ).

Are you planning on making an exchange that supports SNIP20s, and you pay APY for staking ERC20 from trading fees income?

My understanding is that bridge mining incentives are paid from the Secret Network Ecosystem fund. Bridge mining will last a total of 6 weeks. There will likely be similar incentives paid from the ecosystem fund to LPs of the upcoming AMM, and maybe even more incentive programs in the future.