Indigo is a Tonkinese and they often play fetch but Madiba learnt from watching her, we suspect. I rewarded the cats when they showed this inclination as mostly it is a much fun for us as for them. I just found a toy/object they really loved, had a really good play session, tossed it a fair distance away and encouraged them to bring it back. My husband jokes about them never retrieving anything useful - like his slippers, or chocolate from the fridge for him to eat. In reality, they trained me to continue the play session by bring the object back to me as I didn't do anything special.
Given your posts on clicker training if anyone could train their cats to fetch I'd think it would be you.