I agree that Twitter in its current form would be terrible for argument mapping. However, in one sense it would be beneficial to limit a single claim or assertion to a certain character length, provided that there is a way to represent the overall argument as a tree or web of assertions. The limitation would force the arguer to organize their elaboration.

Elaboration is crucial to productive arguing, but it's something the reader should be allowed to hide during their initial encounter with the argument.

I hope something like DebateGraph.org catches on as the infrastructure for arguing in the future.