Historically, the Mac mini has basically been a headless entry-level (non-Retina) MacBook. Now that the non-Retina MacBook is gone, the likely base architecture would be that of the MacBook Air.
My guess is that the next-gen Mac mini would have Intel HD Graphics 5000 by default, with possibly a BTO option of the Iris Pro chip on the high-end Mac mini model, although a more likely option would be a quad-core CPU with bigger cache memory (and possibly a higher clock rate) with the same 5000 graphics. The Mac mini has never been a gamer's box even when it received discrete graphics.
Regardless of the specs, talk about the 4600 series doesn't make much sense (particularly since it seems like a backwards step from the 5000); it's another model line to support, and Apple has historically reduced the number of graphic architecture variants within a given product year for simplicity (and likely engineering efficiency).
Apple typically does not release new products after mid-November due to the U.S. holiday sales season, so if we don't see a new Mac mini in the next week or so, it is highly unlikely that we would see one until sometime in January 2014 at the earliest.
There are no current rumored reports of the Mac mini inventory drying up in channel reseller stores or overseas -- making a silent refresh next week less plausible -- so my gut feeling is that the refresh will wait until early next year, and Intel HD Graphics 5000 will be the featured graphics architecture.