i've worked for a company with a plan that offered something like this, however there was an additional fee on top of whatever the costs were. And like the sibling comment says, you get the public etfs, which wont get any bulk savings(oh how i miss my 0.02% ER institutional shares). You are unfortunately still stuck going through the company the employer chose. Very rarely you can get a plan that allows you to roll over while still employed, so if you did that say, annually, you could self direct then.
employer matching was separate, you and the employer add money, then you choose what to do.
IMHO, 401k should go away and the deductible limits on IRA should be raised to compensate and let people do their own thing.