They seriously couldn't make a television show about
Khamûl? I know Khamul was a villain, but you could've made him a super sympathetic misunderstood hero who just happened to have been seduced by Sauron and turned into an undead monstrosity. We know absolutely nothing about him in canon besides his name and general region of origin, so writers would have basically free reign to describe his character however they wanted. Want to make him a homosexual in a homophobic society who joined Sauron because Sauron promised to legalize gay marriage? You could write that and Tolkien fans couldn't argue it wasn't true to the canon because Tolkien never wrote about his backstory.
Or the
Blue Wizards, who actually ventured into the South and East and convinced the Southrons and Easterlings to revolt against Sauron? If they hadn't done that, then the Southrons and Easterlings would have conquered Middle Earth all by themselves even after Sauron lost. You could make a series about their adventures and cast an entirely non-white cast. The Blue Wizards could easily be played by non-white actors, because it makes sense they would assume the forms of the people of the regions they're visiting. You could even cast them as women of color and I think most Tolkien fans would just accept the gender change with only a minimum of complaining. They were supposedly male, but it's not like that matters given the general lack of info on them.
And fans would probably rejoice.
You could have black Eastern dwarves by casting black albino actors, which would also provide albino representation and jobs for black albinos. And honestly I doubt people would complain if there were Asian and African featured elves living in the South and East. Maybe they always looked like that, maybe they're half-elves who inherited the looks of their human ancestors. You could even have anti-white racism coming from these non-white elves who use the whole "white elves were a beta test, non-white humans are God's final plan" as a rationale for their racism.
See? It's not really hard to show the diversity that could already exist in Arda without spiting the canon.