Has this completely gone from the game?
Watching the Leeds-Catalans game, Kristan Inu caught a ball in the Leeds in-goal area. As he was in the act of scoring the try, he was clearly tackled in the air by a Leeds defender. If this isn't a clear 8 point try, I don't know what is!

They changed the rule so now it has to be literally in the split second when the ball is being put down.

Can't be much more split second that contact in the air as the ball is grounded?

According to the RFL it can.

Sam Tomkins got knocked out while diving to score a try a few years ago and that wasn't an 8 point try

Never a penalty try in my book. Don't think Briscoe did too much wrong; he can't just disappear.

He did make contact once he was back in the floor and Inu was in the air though. It wasn't much, but more or less any contact, deliberate or not, with a player in the air has been a penalty this year,

If it wasn't in the act of scoring, yes, a pen, but I'm happy for 8-pointers to be restricted to serious foul play by a defender, like going in with the feet Billy Slater style.

Possibly wrong but I was under the impression that once the ball has bounced, Which I think it did in this case... then the tackle in the air rule isn't applied?

As Moto said Briscoe didn't do anything wrong. Inu jumped over the top and onto Briscoe.

As for 8 point tries in general, I agree they're hugely underused. For some reason the authorities appear to want to get rid of them. I think they should be used more often to prevent foul play on try scorers. The most prevalent being high tackles and use of the feet/legs/knees by a defender.

Correct. Not sure why this rule exists though, in the air is in the air regardless of how the ball gets to the man.

I'd prefer to see the rule remain under-used. I don't think I could bear all the fannying about by video refs that would result, were its use revived. They'd be analysing the minutiae of the most trivial of fouls from now until kingdom come.

Yeh It is a weird one. I'm not sure if they applied the rule for safety reasons to stop players being tackled in the air and landing in awkward positions but like you say.. if the ball bounces high enough for someone to need to jump up then the resulting tackle in the air is going to be no different, regardless of it bouncing or not.