And telescoping wings were done in the 70's (Lookup FS-29), as well as the extending TE to change area and camber (FK3 and Sigma)http://www.betsybyars.com/guy/soarin.../70-sigma.html

Mechanics on both of them created quite a workload for the pilot.

By the time the configuration change was complete, the glider had sailed far beyond the thermal.