Although we already have a prefetching service ApiEntityLookup it is only used in a prefetching term lookup currently.
The hook that we use for formatting summaries only knows about 1 summary at a time and thus can not do prefetching.
(This relates slightly to T257912 which also tries to have some hook run on these pages at a higher level)
The hook may end up being the same as the one there, but may also be different.
When one of these pages is loaded (where this hook runs)
As few API calls as possible should be performed
By using the ApiEntityLookup to pre fetch and batch the entity lookups