"[M]any courts have struggled with whether nonqualified deferred compensation plans qualify as 'top hat plans' exempt from the bulk of substantive ERISA requirements. Generally, these cases have focused on whether a plan meets the ERISA definition of a top hat plan, meaning it covers a sufficiently 'select group of management or highly compensated employees.' In recent years, there has also been significant growth in litigation over other issues with respect to these plans, including both procedural and substantive issues."