Have you considered to jettison some of the batteries during and/or after take-off?
Probably not just drop them, maybe a controlled glider or similar, plus what are the posibilities for an in the air charge by tether to another plane?
Final super radical idea, have some iflatable high chord wings for take off at low speed high drag and lift, then ditch them somehow once at altitude and can do a anouever with stored height to get speed. (Or a lift blimp).
Love the brainstorming. As you mentioned, "decoupling" the cruise mode from the takeoff mode could make a lot of sense. One of the most innovative and feasible solutions I've seen is from a former YC company called Talyn Air https://www.talyn.com/
They have a nice animation showing the lifter and the cruiser vehicles.
If the mass fraction of batteries on the plane is bounded by some not too large number (I'd guess at most ~30%?), then your range increase will be less than that. Given the increase in complexity, risk and additional hardware neutralizing those changes, I don't think battery ejection (via gliders or anything else) is viable.
Mid-air refueling (e.g. via drones swapping batteries) would be more plausible, but it still seems like a risky and complex operation -- think of turbulence, weather events, remote flight routes, etc. (but maybe it's possible to get it reliable enough).
Probably not just drop them, maybe a controlled glider or similar, plus what are the posibilities for an in the air charge by tether to another plane?
Final super radical idea, have some iflatable high chord wings for take off at low speed high drag and lift, then ditch them somehow once at altitude and can do a anouever with stored height to get speed. (Or a lift blimp).
As you say, the take off is where the problem is.