This is a question that has been raised in every generation of the Unreal Engine, and it is definitely not in the works. Lock-step execution can only work if every engine system on every platform is designed for absolutely deterministic execution. That’s not the case with UE4, as a big engine with a time-dependent game update model and reliance on a wide range of middleware and a wide range of platform and runtime OS-version and API-dependent optimizations. An engine could be designed this way, but UE wasn’t, and it’s not practicable to retrofit it for a special usage case.
Instead of lock-step determinism, I recommend working with the engine’s network replication framework. This code has fairly good performance and typical internet connections have plenty of bandwidth, so I expect it to be practical for RTS usage.
Also keep in mind that you can customize the engine’s relevancy checks (which determine whether a given object is replicated to a given client) based on the client’s view of the world, which will usually change fairly slowly in an RTS.