Boeing released their new aircraft having Truss-Braced wing type
Actually, Boeing already have own experience related to the joint wing as described in this blog
This E-X concept is more radical than the Truss-Braced type, and type category of joint-wing is shown below 
Fig. 2. Type of Joint-Wing 
Although there were several prototype attempt to materialize joint wing (https://www.secretprojects.co.uk/forum/index.php/topic,4963.75.html), Boeing's one is interesting that there is no project like this in recent years. Boeing emphasized this project focuses fuel saving and noise reduction. From the reference , it might cause non-linear problem for the aerodynamic and stability perspective.
Complexity of the wing shape is caused by tandem configuration of the wing and joint-part generating complex flow configuration while aero-elastic problem also should be considered..
Fig. 3. Pressure distribution of the joint wing and its optimized shape 
Optimized shape of Truss-Braced wing could achieve higher L/D and more payload than conventional shape as described in Fig. 4 . L/D is increased from 26 to 32 however, increase of structure weight is significant. Finally, Boeing current concept is very similar to that of Fig. 5, class of mid-range airliner cruising at transonic speed. Anyway, it is interesting to watch the development of the old-new concept.
Fig. 4. Optimized shape of Braced-wing 
Fig. 5. Optimized shape of Braced-wing similar to Boeing's current concept 
 Cavallaro, R and Demasi, L., 2016, Challenges, Ideas, and Innovations of Joined-Wing Configurations : A Concept from the Past , an Opportunity for the Future, Progress in Aerospace Sciences