I think about 80-90% of the UK can order >1G broadband, fairly similar in most of europe, though some countries do lag behind. Realistically the number of homes with more than 20metres of cat5 structured cabling is very very low (much less than 1%). Typical new builds might give you a CAT5 from the utility cupboard to the TV and study if you're lucky. As such for now it's fine as 10G is 'OK' and even in the case the cabling doesn't support 10G, it should at least do 5Gbase-T.

Most providers are topping out at 2.5Gbps and big part of that is that you can't actually use even that much over Wi-Fi and anything >2.5Gbe consumer side is comparatively expensive/rare and no hard wired cabling in most houses anyway. So as such most ISP routers are 2.5Gbe LAN with only a few exceptions (https://www.choose.co.uk/broadband/sky/reviews/sky-gigafast-...).