With Infinispan's transition to Caffeine to implement its data container, WF should finally be able to offload eviction to Infinispan, by configuring caffeine to use a specific Weigher that returns 0 for non-primary session entries, where max-active-sessions is configured as the maximumWeight. From an Infinispan configuration perspective, this corresponds to a custom EntrySizeCalculator that returns 0 for non-primary session entries, and a maxSize equal to the max-active-sessions. The remaining entries would rely on cascading eviction (i.e. manually evicting from a via passivation callback).
As of Infinispan 9.1, the requisite DataContainer configuration attributes are deprecated - thus we need to lobby to expose the mechanisms for overriding the entry size calculator to be able to ensure this solution will be supported in the future.