TNT in vanilla minecraft has become more useful, it is now able to be dispensed from a dispenser in its ignited form and also returns 100% of the drops of the blocks it destroys.
Gunpowder Barrels (GB) could be made to mimic that behaviour.

Explosions from GBs currently also do not support sympathetic explosions of other GBs or TNT. TNT explosions however do ignite GBs.

Finally, in order to set GBs apart from TNT in a way to not just make it a reskin with different ressource costs, GB explosions could be made to not destroy already dropped items. I have no strong oppinion on what it should do here, just put it out as a thought.

make them lobbable "grenades" for mining that you require flint and steel/firecharges in the offhand for? they do have this handy fuse on the texture :)
totally not for dynamite fishing from a boat

If anything, it feels like Gunpowder barrels are pretty pointless now, except for having a neat texture.
I honestly don't know what to do with them. I could just remove them tbh, given that they are superfluous, but I also do quite like the texture...

Why do i suddenly have donkey kong music in my head?

Or maybe you could turn them into shaped charges for even easier mining. Where the blast just goes in the direction of the face you placed the barrel against. I know that's not how shaped charges work, but just more drops into the idea pool to set the thing apart from TNT :)

I like the idea of having a defined path of destruction, make it explode in only one direction and rotateable also a bit (minor damage range) in the other directions