Answer
That four-core ceiling is a capacity planning number as much as a licensing detail. A shop sizing an IBM i partition on the S1112 needs to plan interactive and batch workload within that boundary, which means workloads that are growing quickly or that already strain a four-core allocation on existing hardware are poor candidates for this server regardless of how many total cores the box has. The remaining six cores are real capacity, but only for partitions running Linux, AIX, or VIOS, not for scaling IBM i further on the same machine.
Buyers who expect to outgrow four IBM i cores within the server's useful life should compare the S1112 against Power tiers that support a higher IBM i core allocation, such as P10 or P20 class servers, rather than assuming they can upgrade in place later. It is worth asking a reseller directly what the migration path looks like if workload does grow past the four-core boundary, including whether that requires a new server purchase, a new IBM i entitlement, or both, since that answer affects whether the S1112 is a genuine long-term fit or a short-term budget decision.