As I understand it, in practice it’s often about state income taxes, not future plans.
And future plans are also often about state income taxes - the weather isn’t the only reason that Floridians don’t retire to New York while the reverse is very common.
It’s not one the states in question, but I did find some information for Ohio voters:
http://www.sos.state.oh.us/SOS/elections/Voters/voterEligibility.aspx#qualifications
It seems that at least in this case, RealityChuck’s suggestion that a parents’ address is valid does not seem to be accurate.