Frankly I don't see one. Politically impossible. There was a short window of opportunity near the top of the bull market, but it's gone.
Government undermines everything it subsidizes. Saving for retirement is no exception.
A nasty feedback loop has been powering up over the last few decades: Government subsidy of retirement will require greater taxation to fund obligations, and removes old age as an incentive to have (and be nice to) children. In order to maintain the social niche in which they were raised despite increased taxation, people delay having children, and have fewer when they do. This erodes the future tax base, requiring once again greater taxation per person.
The system will collapse of its own weight.
The one way out I see is massive immigration -- particularly immigration of the poor. It costs very little to raise a child in poverty, so the tax disincentives for having children is much less for them. But this does nothing to address the long-term destruction of the middle class, and is the road to looking more like, well, Mexico.
The Framers gave us a Republic .... saying, "IF you can keep it."