Yeah, that's my thought too. I very much doubt that too many politicians would be able to make a platform of the con or ex-con vote, except in a few small town in Texas that have massive prison complexes.
I think that everyone that has reached the age of majority should have the right to vote, if they can follow the basic, simple procedures to at least enter a polling place to cast a ballot.
For those convicted of a crime with a chance of parole or release at conclusion of sentence, they'd have a choice. Remain registered to vote where they last lived before being incarcerated, or register to vote where they now live. There would be rules that outsiders couldn't visit prisons, the most that they could do would be to mail literature to prisoners. There would be no polling place in the prison, prisoners would need to absentee-vote, most likely by mail. Prisoners convicted to life without parole would only be able to register at their new permanent address. The main reason for these particular rules would be to restrict the possibility of prison staff tampering with the vote or compelling prisoners to vote that have no interest in casting a ballot. If the prisoner doesn't work up the interest to register to vote by mail, then the prisoner just doesn't vote.
I'd also modify the nature of voting in-person at polling places. One could show up to any polling place in the county or perhaps in the state, present ID, and receive a ballot that reflects one's voting district. This would prohibit in-person-disenfranchisement by allowing those attempting to vote at intentionally-understaffed polling places to go to other polling places to vote.
All ballots would be paper with optical scan, and randomly an entire polling places' ballots would be manually audited to verify that the electronic count is lining up with what's on paper.