Based on a review of Boeing patent applications in the blog “Things with Wings” of the Aviation Week Magazine, there are some intriguing insights into possible future airliners.
One of the most ‘exciting’ concept described is what at first glance looks like a return to the Boeing 707 days, with a similar sized 4 engined jet.
US patent office drawing of Boeing battery pod concept
However the outer ‘engines’ are actually battery pods for a hybrid electric-liquid fuel low carbon emission airliner.
With this configuration, in the event of a battery incident -like those that grounded the 787s- the battery pods will be ejectable. “Hopefully not over inhabited areas.”
Based on the article “Boeing patent for 4 engined jet not” published in Plane Talking blog