While the staking system may be modified with future governance initiatives, the initial pools require BPTs created from the MPL:USDC Balancer pool. The tokens in the stake locker contract must be easily liquidated in order to provide cover for lenders under default conditions. In order for this to happen:
MPL needs a liquid decentralized marketplace
Liquidation of MPL needs to produce the lending pool liquidity asset (USDC)
For these reasons, the MPL:USDC 50:50 pool will be the first pool token used for staking as pool cover for the Maple protocol.