Thank you for bringing a more in depth and comprehensive view to this subject. Some of which I did not know or understand, and most of which is unassailable.
As I understand it, in many cases, expats working abroad do not owe taxes to the US. If you meet certain requirements, the IRS cuts you a break with the Foreign Earned Income Exclusion, the Foreign Housing Exclusion and the Foreign Tax Credit. The US also has tax treaties with over 60 countries. Tax treaties vary from country to country. Treaties also generally provide U.S. athletes with special exemptions from the foreign treaty country's income tax, although you still must file.
I would comment on some things. You've said some leagues "are likely to respond by trying to schedule their seasons in prioritization-compliant time frames". I'm honestly curious, without any cynicism here, as to why you think so? How would it benefit a foreign club to do so; to alter their entire season, which would have an effect on their entire league, in order to comply with the WNBA's time frame? You've said the "worst known effect of prioritization is the attempt to prevent players from training with their national teams for the customary length of time". Yet as I've understood it, obligations to national teams will be given exceptions. Also, as I understand it, the league can suspended without pay for the entire season any player who does not report, which may really hurt those players not making Taurasi or Griner money.
Your said you see no evidence that the financial situation for basketball outside of the United States is in positive shape. You're perfectly correct, and I can't disagree with the evidence. Yet it's been my understanding that it was slightly better than the situation here in the US before the pandemic, and the rate of growth, although slow, had been slightly better than here in the US until last season. It's also my contention that the TV viewership increase in the playoffs seen by the WNBA last year, a whopping 63%, was directly due to the pandemic and TV broadcast availability, and that investors are banking on that increase to continue in a non pandemic world. Fan attendance creates little income neither for the Association or anywhere overseas. Indeed, I see no evidence that the financial situation for basketball anywhere is rosey for pro WBB. EuroSport 2 TV broadcasts only one game per week in Europe, so those numbers are hard to judge, and certainly cannot compare to what is broadcast here in the US.