My vote would be to keep all the original GPL licenses in Pd vanilla's expr, and to remove the LGPL readme. GPL was the licensed under which expr was originally released, so we can reasonably assume all the copyright holders agreed to that license.
If the consensus was that it should be changed in order to accomodate Pure Data builds on IOS, then everyone who wants to use expr on IOS should pool their resources and hire a lawyer to explain what is and isn't allowed under the LGPL and Apple's TOS. The lawyer should also find out if it was indeed possible to change the license to LGPL in light of what Miller brings up about the original licensing.
That's two unknowns wrt LGPL expr, and they won't be solved by revising the source nor IANAL discussions.
Best, Jonathan
Cheaper and simpler than talking to lawyers would be simply to write a new compatible one. On the way it could export an API so that other objects could evaluate expressions (you could embed them in messages, make a Max-like 'if', maybe have a thing that creates objects with expr-calculated creation arguments, etc).
cheers M