While there's still some unknowns (esp. price) that could affect market share, on a global basis we should always expect PlayStation to beat Xbox globally barring something going very wrong on Sony's end. Even with everything going in MS's favor last generation, the PS3 still sold at an overall faster rate than the 360 on a global basis and most likely edged out the 360 by time the two systems were discontinued (we never had a true final count for the 360, but it was unlikely to have sold what it needed after the last sales update to tie the PS3). While the 360 dominated the PS3 in the U.S. and UK, it struggled against the PS3 in mainland Europe (where there is a tremendous brand loyalty to PlayStation) and sold poorly in Japan.
With that being said, I think it's still possible for things to shift slightly in MS's favor. Assuming equal prices and no real screw-ups between now and launch (and both Sony and MS have been playing it safe this go around), it would not surprise me if the PS5 and XSX are in a dead heat in North America, a market that is known for being very fickle with no clear brand loyalty. Considering how often the UK market is a mirror of the U.S. market, it's possible that could end up being the case there as well. But the PS5 will dominate continental Europe, and Japan will almost certainly continue to mostly ignore Xbox. I could see the final split between the two potentially ending up something like 100-110M for the PS5 and 65-70M for the XSX.
And I do not share the author's pessimism that the console market will experience significant shrinkage. While combined PS4+XBO sales in the U.S. will likely fall short of combined 360+PS3 sales, that gap can be attributed to the simple fact that the 360 had eight years on the market instead of seven. In terms of overall sales rate, the PS4 and XBO have had very strong combined sales in the U.S. that have outpaced what the PS3 & 360 did in their first 6-½ years. In Europe, meanwhile, combined PS4 & XBO sales should end up at least a few million units better than combined PS3 & 360 sales. There has been some shrinkage in Japan, however, but not enough to have a significant impact on global sales. The console market in general seems to be roughly zero-growth. I don't expect combined PS5+XSX sales to be less than those of combined PS4+XBO sales, but I don't expect them to be higher, either. I think they'll be roughly flat, assuming another 7-year cycle.