The last two remaining Starwood properties that were not SPG participating have finally changed their minds (or probably their contracts were renewed that required them to become SPG participating).
Both are category 6 properties requiring whopping 20,000 Starpoints per nights.
Starwood used to have a lot properties in Dubai that were part of the chain, but were not SPG participating. This has gradually changed and now there are no Starwood hotels left that wouldn’t also be part of SPG.
Whether these properties make any sense to use Starpoints at the 20,000 points per night level is another questions, however.