With the new Cap increases they can probably afford to pay Jackson or Green but it would make more sense for that cash to go to Green...
The big cap jump is going to be the following year.
Why would it make more sense to pay the money to Green?
1. Jackson is younger.
2. Jackson is going to be a restricted free agent which usually keeps teams from overpaying, while Green is an unrestricted free agent and you may be forced into overbidding or losing him for nothing.
3. Jackson backs up a player that has lost major time due to injuries each of the past three seasons including one year in the playoffs whereas Green backs up the Durant who has only had this one major injury thus far.
4. OKC has no quality PG depth after Jackson while without Green, they still have PJIII.
If they are going to pay one, IMHO it's Jackson and I don't think it's even close.
However, they are not even going to pay one. Either one will put them over the tax threshold and if you wouldn't go over that threshold for James Harden, you certainly aren't doing it for Jackson or Green.