The 787 has great potential, just off to a bad start thus far :(.

I think the whole idea would be to taxi with the wings up, then put them down before entering the runway for takeoff.

 

I doubt it, the only reason you need the folding wingtips is to fit into a smaller gate, taxiing is not a problem.

Depends on the airport, really. If they have taxiways which are not Category F approved, but are Category E approved, and need to be used, they can just as well taxi with the wings folded up.

I thought taxiways also were rated based upon weight of the aircraft based on pounds per square inch. Thus the 777 has six tires on each of its main gear, evens out the weight.

 

Boeing certified the folding wingtip, American Airlines wanted them to fit into some of their tighter gates. If memory serves me right, I believe they made a demonstrator of the conceprt but not sure it was ever built into any of the certifcation aircraft. Boeing did not build a dedicated test fleet like they did with the 787s; they were all customer delivered aircraft. American never ordered any.