Alas, macOS doesn't support any native scaling other than 100% and 200%. So if they did release e.g. a 27" 8K monitor, the text would either be too small, or they'd have to use bitmap scaling to make it bigger in which case there'd be no advantage of having an 8K monitor.
(EDIT: To clarify, all other scaling factors are done by rendering at either 100% or 200% and doing bitmap scaling up or down. By bitmap scaling 200% up up to e.g. 250%, things are bigger so that's good, but there's no extra detail being displayed, so you're wasting the resolution of your monitor. You might as well buy a cheaper monitor with fewer but larger pixels.)
I really don't understand why they don't either (a) adopt Windows' approach of allowing rendering directly to any arbitrary scale, or (b) at least introduce a 300% mode with bitmap scaling analogous to their 100% and 200% modes.