I don't see Ethernet being dropped, but I can see Firewire 800 being replaced (I think it's the only Mac that still has Firewire now?). I'm unsure if it'll see a jump to Thunderbolt 2, but two ports will be welcome.
Processors will definitely be Haswell, probably Iris graphics on the whole range, hopefully Iris Pro on the high end model. Might have Iris Pro on the server model too, as Crystalwell can accelerates both CPU and GPU depending upon their workload.
Definitely wireless ac and latest Bluetooth.
RAM is another slight question-mark, but since the entry level iMac has 8gb of RAM now I could see the Mac Mini getting the same 8gb as standard, especially since it helps with the integrated GPU, particularly with the improvements in Mavericks in how it allocates the RAM.
I don't see an all-new design coming just yet. If they do do a new design though then I can see it dropping the second slot for the hard drive in favour of using an mSATA or PCIe SSD for Fusion Drive options, this will allow them to make the machine even tinier, maybe even ditch the square (someone suggested round in another thread, and it seems likely to me). But again, I don't see that coming from the next update unless it's delayed till the next media event, but I'd expect (and hope) for the more modest spec-bump only update to just come out quietly.