My reaction to the abstract was that the idea of a "gravitational towline" must be crazy...but then I read the paper. A massive spacecraft, applying a miniscule thrust over a period of many years...yeah, it seems reasonable, and you don't have to worry about whether the internal structure of the body will support a physically-attached engine.

Clever fellows, to substitute subtlety and a delicate touch to solve a problem everybody thought would be humungously difficult using brute force.

Now I want to know this: How massive would the tug have to be to move one of those conjectural mini-Earths from the Oort Cloud into Sol's habitable zone? Big, I'd say, which suggests a hybrid approach: Find a moon-size body solid enough to support physical attachment of the thrusters, nudge it near your Earth-size body, and apply full impulse using the moon's "gravitational towline". Or just look for an Oort-Earth that already has a moon!

I still think it'd be cool to reengineer the inner Solar System...