What say you era?
Resetera being a gaming forum, I expect many will say the XSX will outsell the XSS... but for the more casual crowd the XSS is a really good option.
Hell, maybe Microsoft themselves expect to sell more XSS units?
Going forward, xbox is gamepass. The Series S has great potential as a 2nd machine, but that probably doesn't really kick in until it's been around a little while and people look outside their current ecosystems.
Not many want to face the reality, but Series S is the next gen xbox hardware, it's the baseline targetted at the masses. It'll sell the most by a long, long way. The Series X is an enthusiast model mid-gen refresh that just happens to arrive day 1. In a similar manner that the 1x was to the 1/1s, it'll be adpoted at same sort of ratio in the long run. Of course this won't play out in the first 6 months or so, as people who buy in to next gen early are generally enthusiasts, and they'll want the proper box. There's little to persuade casual players to jump to a new generation in times of cross-gen especially when first party has very bleak schedule in the short to medium term. For the next half year Series X will do far bigger numbers in terms of ratio than it will lifetime.
If we're led to believe both models are taking a financial hit, especially the low tier one, there's a case to be made that the price differential might ease favourably the Series X's way over time, but this depends to a larger extent where pricing goes on each unit's parts list... we might see a 1tb Series S unit before we see any price discounting, for example (personally that'd be something I'd be looking for around 2 years from now as internal studios close in on their big releases).