I guess the question is, what is the point? We can already take any portion of our pay and purchase bitcoins with it, no need to set up direct deposit and all that.
Perhaps more importantly, bitcoin is simply too unstable for this at this time. Speculating in bitcoin is all well and good, but I don't know that too many people want to gamble say, their next mortage payment on it.
The volatility of bitcoin is one of the reasons I wanted to be involved with a payroll-to-bitcoin service. By purchasing smaller amounts of bitcoin over time you lessen the risk of investing a large amount in a single investment at the wrong time.
The idea is that you would not take all of your pay in bitcoin, but only the portion you wanted to invest.