Xbox One still accepts discs. next gen will also still accept discs. though the next gen will come in two tiers, like the Xbox one S / X. the Lockhart will supposedly be a discless version and less expensive. while the Anaconda version will still be able to play discs. it's possible Lockhart will also have a disc, and they make a third Xbox One console that is discless.
but, with stores still selling discs - best buy, game stop, walmart, Amazon, etc. it's going to be years if not decades before everything is completely digital.
i'm the same as you, i prefer discs. it's rare, though possible the system and service could eventually die out, and unless you have games installed on your device, you won't be able to play them all if they are all digital.
but i don' think we have to worry about that for a while.