Any political voting system will need a trusted third party to run the voter registration/identity system, so I doubt the lack of practical homomorphic encryption is blocking this. There are other voter-verifiable systems that don't rely on HE for trustworthy counting:
https://www.chaum.com/publications/AccessibleVoterVerifiabil...
The major problem with online voting is that people can be coerced into voting against their wishes outside the watchful eye of election authorities. This may be worth the increase in voting ease, but it's where the real debate is.