A lot has been written about what Apple's (NASDAQ:AAPL) Mac launch schedule is going to look like. I believe that with Intel (NASDAQ:INTC) having formally launched Broadwell-U (15 watt parts), the new Retina MacBook Air isn't too far away. I also believe that since Intel has also announced 28-watt Broadwell-U parts, a refresh of the 13-inch Retina MacBook Pro is likely just around the corner, too.

That being said, while the chips needed to power the MacBook Air and 13-inch Retina MacBook Pro families are either here or really close, the same can't be said about the 15-inch Retina MacBook Pro.

When should we expect a 15-inch Retina MacBook Pro?
When Intel launched its initial wave of Broadwell chips, it was reported that the higher power 45-watt (and above) parts would be available at some point in "mid-2015." This jives with the Broadwell processor launch schedule that VR-Zone publicly revealed. These are the processors that would go into an updated 15-inch Retina MacBook Pro.

Given Intel CEO Brian Krzanich's comments on its most recent earnings call which suggested that the company wanted to intercept the back-to-school selling season with its Broadwell chips, it seems very likely that Apple will want to have a full lineup of MacBooks -- including the 15-inch Retina MacBook Pro model -- ready to go to capitalize on that demand. 

Why releasing the 13-inch and 15-inch Retina MacBook Pro months apart would make sense
If Apple releases products roughly in-line with when chips are available, then I would expect the rumored new Retina MacBook Air, as well as an updated Retina MacBook Pro 13-inch, to be available by the end of the first quarter of 2015.

Then, I expect that Apple will update the Retina MacBook Pro 15-inch as well as the entire iMac lineup to Broadwell in time for the back-to-school season with Broadwell. There is a cheap iMac in Apple's lineup that uses the lower-power Intel processors found in the MacBook Air/13-inch Retina MacBook Pro that could get updated sooner, but Apple might as well wait to upgrade the entire iMac lineup at once.

iMacs likely to get upgraded, too
If Apple updates the MacBook Air and the smaller Retina MacBook Pro separately from the larger Retina MacBook Pro, then I'd expect the latter to launch alongside updated iMacs. The leaked VR-Zone roadmap claims that all of the higher-end Broadwell chips come at the same time, so I don't see why Apple wouldn't go ahead and update both the 15-inch Retina MacBook Pro as well as the iMacs at the same time.

It should be an interesting year for Mac
All told, I think it'll be an interesting year for Mac. If I had to guess, I'd say the Retina 5K Mac will get a new Broadwell chip but keep with the same industrial design. What Apple does with the regular iMacs and the MacBook Pros -- whether it does new industrial designs or just upgrades internals of the existing ones -- isn't clear yet. We'll find out soon enough, though!