The October 1 deadline is the deadline for establishing a SIMPLE plan, not a SEP plan. It makes no sense in this case to have a SIMPLE plan rather than a SEP plan. Since the individual elective deferral limit of $18k is already maxed out with the 401(k) elective deferrals, no elective deferrals would be permitted to a SIMPLE plan. Contributions to a SIMPLE plan would be limited to a 2%-of-compensation employer contribution.
