Two factors appear to be driving the gradual emergence of partnerships between European short/medium haul LCCs and long haul operators (full service and low cost).
First of these: European LCCs are able to operate at a significantly lower unit cost on short/medium haul than most competitors with long haul networks. The provision of very cost efficient feed is an attractive idea to long haul operators, particularly as LCC networks expand to include more primary airports.
However, most LCCs, particularly the independently owned operators, are reluctant to enter into codeshares, to adapt their networks and schedules and to modify their business model in any way that might add cost and complexity in order to accommodate long haul partners.
The second factor is the emergence of European long haul low cost (LHLC) airlines. Just as with full service long haul, LHLC generally requires feed. Norwegian, Europe's leading LHLC operator, feeds itself from its own short/medium haul network, but is still open to partnerships with others (as exemplified by its participation in easyJet's 'Worldwide' connection partnership).
The CAPA Low Cost Long Haul Global Summit in Seville, Spain on 4-5 October 2018 will include panels on partnerships between LCCs and long haul operators.