Availability of dual-stack consumer equipment
I recently had the ‘pleasure’ of using a Netgear router/modem as a short-term replacement for some failed hardware. It's fine as a dumb switch and wireless AP, and used as such it'll happily handle anything IP – but try to get it, as a router, to do proper dual-stack and, well, you'll quickly find that you need something else.
Yes, it'll do IPv6. But only if you use 6to4 or you forgo direct IPv4 to the outside world: the former is laughable, given an ISP which provides IPv4 and IPv6 addresses, and the latter is… well, let's just say that it has one or two problems.
Thankfully, I'm now back to using my preferred setup – a modem in bridge mode and a small Linux box doing the PPP termination and proper dual-stack.
There's good consumer kit out there, I'm sure, for those who want something which does dual-stack properly and which works with minimal configuration. It's just a shame that other kit appears to be much more readily, visibly available.