The rumor is Apple Stores have been told not to expect anymore shipments of the Mini. So that means either Apple is killing the Mini or planning a major revision. Hard to say since the Mini isn't a big seller for Apple. It seems suspicious they would stop shipments 3 months before the replacement model but if sales were low it would certainly make more sense than building a bunch of new Minis right now. Apple has also shown a willingness to take a short term hit when introducing new products. The original iPhone was unavailable at least a few weeks before the 3G launched. Could be the same situation here.
I guess the other possibilities:
1) The Mini is getting a total redesign -- perhaps more in the flavor of a delux AppleTV. If the rumors are true about Apple introducing TVs running ATV software it would suggest they are looking to expand their set top / living room presence. It would certainly make sense to offer the existing AppleTV at a much lower price point. $149, $99 even. Subsidize it with an iTunes gift card at very least. If Apple ever gets an iTunes Subscription model going the AppleTV should be $99 or less -- free with a 2 or 3 year subscription.
2) The Mini is turning into a mid-range desktop Mac that everyone wants. Using the same industridal design of the new MacBooks with the usability of the original G4 tower would be quite nice. NVIDIA chipset + 2xPCI-E 16x. Dual core or Quad core options. If they go this route they should introduce a 20" LED cinema display too and offer a decent discount on bundled computer + LCD configurations.
I don't believe a mid-range Mac tower would cut into sales of the MacPro. People who are buying the MacPro truly need every ounce of power. They won't be downgrading to a quad core when they can get an octo core MacPro. The price delta would likely be in the same range as the MacBook vs. MacBook Pro and there's absolutely no indication to this point that MBP sales have been hurt by the lower price point / power of the MB.