Hey!
Even if the claiming process is going to happen in Ethereum mainnet, the transaction is unlikely to be very gas intensive, as it will be a simple claim function. We can see what the final gas cost is going to be, and if necessary, the rewards expiration time can be revised by the Governance Committee during the initial 6 epoch period. And even then, with new chain deployments coming in the future, additional options would become available in the future.
The importance of fee expiration in the redistribution regards ensuring that funds are not lost on addresses that are lost/inactive. Without the expiration period, many of the protocol fees will be permanently lost, bringing a large source of inefficiency to the new system.
Regarding the balance booster, I think it’s a good opportunity to give people that also have PSP on other chains a boost while we port PSP 2.0 to other systems. The reason we are also including balances in ETH is because it fees unfair to boost all other chains but ETH, but we can change this idea if needed.