I can't be the only one who's hoping and waiting for a Haswell Mac Mini. Anyone else?
In the short-term: a refreshed MacMini released at the same time as the Pro might distract potential new Pro customers who just want a 'headless' machine with a decent CPU, better graphics than the current mini and dual monitor support. Long term, self-cannibalising isn't such a problem for Apple, but when you have a brand new product line you want to give it a clear run for a few months.
Or, to put it more brutally, lets see how many MacMini customers get fed up waiting for the refresh and buy a Pro...
This depends on the pricing of the Mac Pro. It may be $3000+ only true Pros need apply, but true Pros will be waiting for things like improved OpenCL support in third party apps and a better range of non-vapourware TB peripherals (...and a few won't ever be convinced to give up their big box o' slots) and won't be queueing up to buy on day 1. If I were Apple - given this new Pro is supposed to be much simpler to manufacture - I'd be looking at pricing it lower than the current Pro to attract new "prosumer" customers who might not strictly need Xeon/FirePro.
I wouldn't bet too much on it, but I still think there's an outside chance of the Pro coming out at ~$2000 (so you've got enough change from the cost of an Old Pro to get a nice external HD rack).
Other issue: Thunderbolt 2. Intel said that the TB2 chipset will only be available in small numbers at the end of this year, scaling up in 2014. With every Mac Pro needing 3x TB2 controllers, I think that's where Apple will be putting whatever supplies they can get this year. So I don't think we're going to see TB2 in anything other than the Pro until about next summer.
Also, that may mean that its not worth (e.g.) re-designing the Mac Mini mainboard until they're ready to go to TB2.