While this is probably officially considered a 'bug' I think that the length this has been in the game and how much the current community accepts it AND makes content involving it means it qualifies it as a feature. Redstone, particularly slime-block based innovations, are a very large portion of the community, and there are many tunnel-boring machines and quarry miners that have been built and uploaded to YT.
If Mojang decides to keep it removed in the final version, it is going to break any large-scale moving block-breaking machine that is realistically createable. You can't use dispensers, since you have denied us moveable dispensers while allowing all other versions to have them. And you can't fully do everything by hand, either, since a lot of these require more than 1 launcher.
I guarantee you that if this happens, 1.13 will basically be the 1.9 update of redstone. TNT duping is probably the most aggressively patched reoccuring bug, as opposed to harmful bugs like Xraying. Given that it really hurts no one (beyond deliberately malicious use, which would be like removing swords because Grumm's son got killed on a hardcore server), and plenty of people like it, why is it being removed? What does it do besides flip off the technical side of minecraft?
"But it's used in griefing!(insert jumbled mess of 1s and
[media]"
Again, see Grumm's son. If this is realms/etc, just don't be an idiot when inviting people, and make backups. For servers, there are plenty of easy plugins to get to disable TNT in certain situations, especially with the average technical skill of a server OP.
"But... but.. ITS DUPING REEE!"
For it to honestly do something worthwhile, it takes a pretty big machine, as opposed to some other bugs, like, I dunno XRAYING BUGS, which seem to pop up almost every update. For TNT duplication to actually be efficient in situations such as quarries, you need to spend thousands of blocks on it (see ilmango's quarry and look at the machinery behind it.
"It's unfair to people who actually dig!"
Actually it isn't. Digging gives you more precision and better ore ratios/less byproduct than tunneling and quarrying. They have different pros and cons, and honestly, if somebody spends 5 hours making a few quarrying modules they deserve the loot. Not to mention screwing up 1 single block can kill the whole machine, as opposed to, well the mining for that stage in the game, which is generally ench diamond pickaxe with ench diamond armor. Hard to mess up.
dude I know it isn't a bug report but there isn't really a place where I can publicly speak to Mojang employees without waiting 10000000000 years for one to pass by the minecraftforums