AMD does seems even more attractive with the Ryzen but the brand gives very little selection of Mini-ITX motherboards for those wanting to switch from Intel.
For me, it would mean I would have to get a new case, as well as a new motherboard. Maybe even a new PSU.
You would need a new motherboard either way, as the Ryzen CPU doesn't fit into any of the older boards.
Same goes for the new Threadrippers, they need a whole new board, not even Ryzen boards could hold that beast.
Likewise, you also need an AM4 cpu bracket for some of the older coolers, but some nice chaps also send out free AM4 brackets to suit older coolers.
Then again, some of the Ryzen chips do come with a cooler, some are even RGB ;)
PSU wise, Ryzen doesn't use much power at all, so guess it depends what your current PSU is & what you'd plan to use in new build. If PSU is getting on in age, always worth getting a new one anyway.
There's rumours of a mini board en route, sure saw images recently, but forgot where. D'Oh! hehe.
Case wise, check out Kolink. They have some really cheap cases. https://forums.overclockers.co.uk/threads/introducing-kolink-redefining-affordable-quality.18699374