Apple is having a hard time keeping secrets lately, and it doesn't help matters when the source is Apple's own support group.
Apple's recently updated Boot Camp support document included a list of Macs that meet the minimum requirements for using Boot Camp to install Windows on a Mac. The list included both a mid-2014 Mac mini and a mid-2014 27-inch iMac, neither of which is currently available.
Both references to the new models have been removed from the support page, but if you use Google to search for the page, you may find the cached copy still showing the entries.
The document didn't include information detailing the configurations of the updated Macs, or when they would be announced, but based on the recent release of mid-2014 MacBook Pros with Retina Displays and a 21.5-inch iMac, we can offer some reasonable speculation.
The mid-2014 21.5-inch iMac was designed specifically to lower the price of the least expensive iMac and make it a desirable model for business and school users who just need the basics. It's unlikely that Apple will follow this same philosophy with the 27-inch model of the iMac, which has historically included higher end components and capabilities than its smaller sibling.
The mid-2014 MacBook Pro updates are a better guide to what we'll see in the 27-inch iMac, specifically:
Possible Mid-2014 27-inch iMac Configurations
16 GB RAM as the base memory for all models, with 32 GB available as a build-to-order option.
Updated Intel 9-series Haswell processors will provide a speed bump similar to what the MacBook Pros saw, but with a bit more oomph.
In addition, the 9-series Haswell processors provide a faster connection to an SSD, which could improve performance on new 27-inch iMacs even further.
Possible Mid-2014 Mac mini Configurations
The Mac minis are a real shot in the dark, because they haven't been updated in some time. As a result, Apple won't be able to just drop in a new processor and offer more RAM. At a minimum, the motherboard will need a new design, and if Apple is planning such changes, it's likely that we'll also see a new case design for the Mac mini.
As it's expected to do with the rumored 27-inch iMacs, Apple will probably use the 9-series Haswell processors; what's up in the air are the graphics. Likely options are the Iris Pro graphics from Intel, and perhaps at least one model with a second graphics option, mostly likely from NVIDIA.
I expect to see a pair of Thunderbolt 2 ports, as well as an HDMI port and a good number of USB 3 ports. I think the FireWire port will be gone; the SDXC card slot may also be gone. Its current location on the rear of the Mac mini is a bit cumbersome to access, and SDXC slots are now commonly found on third-party displays and inexpensive USB peripherals.
Of course, there is another possibility. The wayward Boot Camp support document may have listed mid-2014 iMac and Mac mini models that have been either canceled or moved to a later release date. After all, both of these updates were expected to use Broadwell processors, which Intel now says won't be available until 2015.