Well, the earlier Mini-PCs were a good bit more anemic, that's why adoption was slow; I had one or two earlier ones; both were AMD Bobcat cores; one was a 'not quite finished' thing where I took a dreamcast and put a small board in it (Where did that go, anyway?) and the other was a small, almost router-sized box. And both of those were, well... good for most of what I wanted (i.e. 8/16 bit console emulation and basic media/browsing) but definitely constrained. (As a side rant, I still wish AMD didn't kneecap non-console Jaguar parts, that single channel limit always struck me as a 'we don't want to show how much we fucked up with bulldozer' sort of thing...)

As far as mini-pcs... The first Intel NUC was a Sandy bridge, i.e. Gen2, FWIW. And we did have the 'Mac Mini' as far back as 2005, buuuuut that wasn't cheap because Apple.

I think SSDs were another big part of mini-PCs though; it's easy to forget for granted the risks of having a hard drive in a poor thermal environment, as well as the general size constraints one imposes. [0]

[0] - Surrrre, you could use a 2.5 inch HDD instead, but 2.5 inch HDDs almost always were slower than a 3.5 inch HDD (excluding the VelociRaptor, but that would only be more demanding as far as thermal...)