In terms of the actual bug reported here, isn't that the same as HHH-10286 Closed (which has been fixed for months)?

In terms of the rest of the discussion (unifying Region and access strategy), that is certainly a possibility. To be fair I have been VERY proactive in trying to get both the Infinispan and Ehcache developers to validate the L2C SPI design. All I ever heard was "looks good" I am ok with this proposed change so long as we all agree across all 3 main providers. So something like:

public interface RegionFactory {
    EntityRegionAccessStrategy buildEntityRegionAccessStrategy(
            String regionName, 
            AccessType accessType,
            Map<String,Object> configValues, 
            CacheDataDescription metadata);

    ....
}

Essentially we fold together building the Region and building the access-strategy.