I don’t think Theymos would consider adding a spell checker as a forum feature. Non native English speakers often use Grammarly to remove errors in their adding. I can’t speak for pc users but for me, I use a mobile to access the forum and my device keyboard highlight’s misspelled words and autocorrects them. Autocorrect can be frustrating when you’re making posts that contain crypto terminologies and slangs that aren’t grammatically correct words like hodl, rekt e.t.c.
I agree with you that theymos won't consider a spell checker because of people don't know how to speak English and write English. If I don't know how to speak English or how to write then U would use translator before I finish studying English and also use grammarly to correct any mistakes in grammar and also the spelling if there's any. Well, there's also local board if a person doesn't want to join English discussions or lazy enough yo study English language.