For some systems either not tractable or not feasible to support paging of ValueSet expansions using the current offset + count approach. However, they would be able to easily support an opaque cursor approach similar to the way Search paging operates.
The proposal is to add
ValueSet.expansion.next uri 0..1
As per paging Search results, the next URLs are opaque to the client, have no dictated structure, and only the server understands them.
Clients SHOULD use the next link, if present, to page through expansion results in preference to using the offset & count parameters. Due to the optional nature of the next link, its absence does not necessarily indicate that it is the last page of results. Instead, as the offset & count parameters SHALL be populated when paging, clients can reliably use the count/offset parameters to determine whether the whole expansion is returned (see http://hl7.org/fhir/valueset.html#parameters).