Please elaborate. If this is truly not possible through development (or if it's too much of a pain), then I'll stop beating a dead horse. Your comment about a skill to summon a "TNT entity" could fix this.
I believe currently, that region protections works by asking whether the block you're trying to break or place is protected, and if you're on the list of people who can break it. By allowing people to place TNT, you'd have to change things to put in a check to see what kind of block it is that you're trying to place for every time you try to affect a regioned block (adding more lag), and if there's a flag against this (I'm assuming they don't want people griefing spawn). This isn't supported by residences, which is a separate plugin used to manage personal regions and spawn plots, so we'd have to scrap it, or have it rewritten in house for the sake of one skill.
How do you place a block and then ignite it? Do you have to light it on fire with a flint and steel since you can't place redstone torches? If you have to ignite it, how long does it last? If it lasts long enough to light, why can't you pillar off of it? What happens if you place your block of TNT in the place of water? You can't replace the water, since you
don't have regions, so you just griefed someone's regions, and that means you can get rid of people's water walls, removing any possibility of protection besides obsidian.
It would also add the possibilities of bugs to regions, that we wouldn't find out until it was implemented, for the sake of one skill.
I think another problem is if miners can summon a lit TNT, then that's basically plaguebomb x 5. My opinion is that it would make TNT less interesting, less hardcore, and unbalanced.
I would like to add that I'm a miner, and this suggestion would benefit me, but I think it would make miner one of the best pvp classes.
EDIT: I misread your comment about cd. I don't know if it's possible to limit the speed at which you can place blocks with skills. But even if it were, there's no reason you'd have to ignite the TNT, it would be slower pillaring, but still pillaring, and griefing