I just had a game with Fanatic of Rhonas and Slumbering Trudge in play. In my main phase, I cast a spell off lands, leaving my fanatic available to tap for 4 mana. In response, my opponent cast Sheoldred's Edict. In paper, I'd obviously respond by tapping my Fanatic for 4 so I could cast some more spells that turn. I didn't get priority or any chance to react since I didn't have an instant speed effect other than that mana ability. There needs to be a better system in place to ensure players get priority in edge cases like this. Maybe make conditional mana abilities hold priority in main phases or something. That'd solve this one at least. Though I think it also would have passed priority if it was just a regular mana dork on an open board into an edict. Permanents with mana abilities already hold priority when targeted, but I believe that's it. That's not enough.