One obvious thing to do would be to reduce the price of the 09 models.
Why? Intel hasn't dropped their quoted Xeon prices.
The 5500 series:
http://ark.intel.com/ProductCollection.aspx?series=39565
(e.g., 5520 $373 )
The 5600 series:
http://ark.intel.com/ProductCollection.aspx?series=47915
(e.g., 5620 $387 )
What Intel did was intro the follow on series of CPUs at slightly higher prices. So that component cost didn't go down. Yeah, hard disk and memory prices may have gone down a bit, but what else has dropped significantly in price ? Any other PC vendors radically drop the prices on old Xeon Workstation configs ?
Apple could shrink their margins, but that is only incentive for the stock price to go down. I doubt they are inclined to go with that option.
As long as Apple can adjust their just-in-time production to keep the inventory of Mac Pros at a relatively constant level they can shrink the supply about as fast as the demand may drop. That keeps the price constant.
There would have to be a radical drop off in demand to get Apple to start pushing price cuts. That won't happen for a while. There may be lots of folks grumbling but most are playing the waiting game.
Other obvious solutions would be to create a desktop line that isn't Xeon-based.
It is called iMac. Apple's position is that solution already exists.
Have an old desktop with an external monitor want to keep? For many, a new higher end iMac and plug in the monitor will work. Now have two monitors and faster machine than 4-5 year old machine for sure. If wanted to replace monitor anyway just have one in new set-up just like old one.
For the folks that misses. If having a tower makes you $50 more productive a month, then in two years that's $1,200. There is you gap between a $1,400 WinPC and a MacPro. If you don't really need Mac OSX then assign that $1,200 to something else. Apple's bet is that you value their set-up that much more.
All the protests of doom and gloom if Apple doesn't provide a mini-tower don't really have much empirical evidence to back that up. Yeah there are folks leaving due to unmet needs. However, there are at least just as many coming in because the solutions do fit.
I say these are obvious solutions because this is what all their competitors do.
Unless you can find a win-win for both customers and Apple you're going to be hard pressed to get them to change their tactics. Much of the "need mini tower" discussions are driven more so by a "win" for the customer than a "win" for Apple. It usually amounts to Apple should take a lower profit and cannibalize more of their own product lines so that the customer can 'win' than something positive for both sides.