You can't yet future-proof for 8K HDMI cables. We know some of the specs, but not enough to cope with whatever might be in the works as future 8K developments.
4K UHD HDMI is a bit of a minefield. There is a spectrum of signal bandwidths ranging from the basic UHD resolution output from Sky through to 4K UHD with HDR and WCG and high refresh rate that (potentially) a higher-end console could output. You could well buy a 7m cable that works just dandy for Sky, but falls over as soon as the signal demands more bandwidth because it's doing HDR or WCG.
Trying to buy a 10m cable that will cope with anything within the 4K UHD realm you might throw at it will cost you a packet. You're looking at either active cable (some electronics to correct for the signal losses), or an optical cable which aims not to lose anything in the first place. Either solution will easily be in the £100 - £200, and maybe more just for something that works reliably out of the box. That, or you can spend a whole bunch of time buying cheaper cables, testing them, then sending them back when you find out they fall over as soon as they're asked to do some real work.
Side note, if you're checking out fibre optic cables online, and you come across claims for signal cable shielding, give the firm and its products a wide berth because they know naff all about cables. Optical cables do not require shielding from electronic interference. They're a light signal, not an electrical one, so it can't be affected by RFI/EMI.
For distance work there are two viable solutions, IMO. Fibre optic or CAT cable with HDMI baluns.
Fibre optic is exactly what it sounds like. The cable converts an electrical HDMI signal in to light pulses. The light is then converted back to electrical HDMI at the receiver end. Fibre is a fixed standard. That means if you buy a 4K 48Gb/s cable today then it won't ever go higher than that if we ever get external 8K high freame rate with dynamic HDR and WCG as external source signals to connect.
The other choice is to run two or three cat cables - probably shielded CAT 6 - and then add electronic boxes on either end to convert 4K UHD high bandwidth to a signal that will travel over the CAT cable.
Using CAT cable leaves more scope for future development. The baluns are doing the compression/decompression work, so you can change or upgrade those end pieces easily as your needs grow. The catch with baluns is whether the boxes drop any quality during the conversion process.
The bottom line is that, for now at least, standard copper-based HDMI cable is right at the edge of the performance envelope for full feature 4K and currently unsuitable for all but very basic 8K.
