Spigot/Forksallow-piston-duplication: true will allow for most of the standard TNT dupers you'll see on YouTube, with the coral fan and all that. However, even with that enabled, it seems like a lot of tick based tnt dupers from the technical Minecraft community will break, unless redstone-implementation is set to VANILLA (we had it on ALTERNATE-CURRENT but it seems like that breaks a lot of farms).