Earlier quoted context omitted.
Sorry for the naive question - but if you're contributing to a 401k, aren't you ineligible for tax-deductible contributions to an IRA? If so, it would seem like an even better business would be getting into administering 401k plans cheaply with employers and then keeping people on the platform post-employment.
I'm pretty sure that contributing to a 401k doesn't make you ineligible to contribute to an IRA, but making over a certain amount of money annually does.
Not a lawyer etc but I don't think a 401k prevents you from making IRa contributions either. Never heard of that.
As for income limits, you can still contribute to your IRA if your income is above the limit (I think that's 125k or so) but the contributions will no longer be tax deductible.
Once you're past that limit, you may as well convert from regular to Roth IRA (this is called a backdoor conversion) so that your money grows tax free.