I've had experience replacing 8 speed components across nearly all parts of Europe, North America and Asia. As of 2018-19, they were harder to get hold of in most places than 9, 10 or even 11 speed, and certainly weren't easier to get hold of anywhere at all. I don't know about Africa or South America but anyone who says otherwise about the continents I mentioned is with the birds. On my trip, I ended up replacing 8 speed stuff pre-emptively, and usually by UPS from the UK whenever I could stay with friends rather than when my kit wore out, so I didn't end up gaining anything.
The argument that freewheels are more easily maintainable than freehubs is even odder. Freehub axles are far stronger and less likely to get bent due to the bearings being further outboard, which is an important consideration for a loaded tourer! You can change a cassette in the field without a vice, which is also a plus point for freehubs. The spline tool is the same for either technology, the chain whip is easily improvised (you'll find
one of these in every motor garage) and all you then need is a spanner! As QG points out, the spline tool will also change your disc brakes, and is a small thing to carry if you're on a tour long enough to require changing cassettes.
Plus of course, if you get the right rear hub, the freehub is pull-out, which is very useful if one of your bearings does suddenly shatter in the middle of the road in India - see below.