I'm not that excited about myRA. This is essentially just a new type of bond (equivalent to the G Fund in the Thrift Savings Plan) offering that you can only buy in a Roth IRA. As one of the other responders wrote, this does not increase the amount of your tax-advantaged space.
And I read one provocative but true post saying that promoting the myRA to low-income people is actually encouraging regressive taxation! This is true for some people. If you're a low-income person in the 10% or 15% Federal tax bracket, then you're likely to be in an even lower income in retirement. People in this profile are probably better off making deductible Traditional IRA contributions instead of what are essentially post-tax Roth IRA (or myRA) contributions.
Regarding some type of wealth/income ceiling for tax-advantaged accounts: in principle I'm for it. I'm not sure what the exact details ought to be.
Let's start with the following premise: we have an income tax because we need to fund our country's government. If you make income, you pay taxes on it. We also have baked some progressive tilts to our tax code. But we also want to encourage people to save for retirement, so we give you some breaks if you do so. There is also some progressive tilts for the tax benefits given to retirement savings, and I think that's appropriate.
Why should a hedge fund manager like Mitt Romney be subsidized (avoid taxes) when he can game the system by injecting insider stock shares in his 401(k) to the point that he has a $100,000,000+ IRA? Why should we subsidize that?
Many tax credits have income phaseouts. Take the child tax credit which is a $1,000 tax credit per child. It's phased out for a married couple filing jointly between around $110,000 - $130,000. While I have mixed feelings about adding complexity to the tax code with these sorts of credits, I do agree with the income phase-out. Why should a billionaire get a tax credit for their children?
Over the last 30 or so years, at least in the US, so much wealth and income have shifted to the extreme upper class, and there are many reasons for it. The wealthy have so many advantages already and I don't see why we should subsidize them even more with tax-advantaged retirement accounts when they are already doing just fine.