This is what my models look like.

@interface FeedItem : RLMObject
@property NSString *title;
@property BOOL isUnread;
@end
RLM_ARRAY_TYPE(FeedItem)
@interface Feed : RLMObject
@property NSString *title;
@property RLMArray<FeedItem *><FeedItem> *items;
@end

Now, say I want display to a user, an auto-updating list of only those feeds that have (1 or more) unread items, in a UITableView.
Ideally, I would fetch it like this:

RLMResults *unreadFeeds = [Feed objectsWithPredicate:[NSPredicate predicateWithFormat: @"items.@sum.isUnread < 0"]];

But, with the above query, Realm throws an exception with the reason: '@sum can only be applied to a numeric property.'

Any chance, we can get support for this operator on BOOL properties?

I have several other use cases for sumOfProperty: to also be allowed on BOOL properties, and in general all 'Aggregating Property Values' methods to be made available on RLMArray.