What concurrency-related challenges would you face with a different design?

With a non-queued design, every single action from end users, such as restaking and withdrawals, needs to be processed immediately by the system, which is not necessary nor cost effective. It is not necessary because the staking operation is not a time sensitive process in PoS systems (e.g. Ethereum staking has queuing mechanism and long delay). It is not cost effective because the bridging cost between the client chain and Imua is not negligible if no batching or queuing is applied.