Ok, it is great 10G pricing seems to have moved down a little bit since I last looked for hardware, although the prices I see right now for the two items linked above are £280 for the 5 port from Amazon, and £440 for the 8 port from marketplace seller. The £320 model is "used" so not a fair comparison, although a potential bargain for someone.
I've not had trouble capping gigabit just doing Windows file transfers. I've not fully tested at 2.5G since my transfers are HD limited to around 220GB/s, keeping in mind that Windows rates are user date, and network rate is for the link, including protocol overheads. Again, for my usage at least, 2.5G is a great stepping stone to beyond gigabit. I'm getting around 2x which helps a fair bunch. I never justified to myself spending much more for 10G to enable that.
My understanding of the Intel 2.5G problem was some kind of timing problem which meant they didn't work with all connected hardware. Not all 3rd party hardware was affected. Since I never owned Intel 2.5G (all mine are Realtek) I didn't look into it much. It is unclear to me if it is an unfixable hardware fault, since it looks like many report it resolved through firmware + driver update of the NIC.
On the earlier suggestion that AMD might try to jump Intel again by going straight to 10G for next gen, I do wonder, what is the relative price like on the interface hardware that will still be required? If higher perf comes at little to no extra cost, go for it. But I'm not sure that will be the case here.