The new Trials of Osiris mode is for real. 3v3 with only revives, no respawn. First to five wins (eliminating the other team entirely) wins the match. Basically a tournament where you are eliminated after three match losses. Try and get 8 match wins for the top gear and 9 in a row for elite gear. They match you based on number of wins so if you have 8 match wins you are likely to face another 8 win team. To sweaty for me.
It's actually really cool and a good way to get end game gear. I suck at it, but oh well. Iron Banner has end game gear drops too so there's that. If anything after the House of Wolves expansion was so lackluster the bulk of Destiny was PvP focused for a while.
They also just did Crimson Days where it was 2v2 and if your teammate got died you got stronger. So they throw some new modes in there now and then. I expect this is really what Division events will be, few day long events to do stuff for gear. I don't think they'll have missions in the Dark Zone but I do think they'll increase the AI encounter rate.
I left before Osiris was added, but frankly, if Destiny hadn't had gear at all I'd probably still be playing PvP just for that Bungie shoot-bang goodness.
As others have said above, the problem with DZ is that its best feature is also its curse.
It revolves entirely around the process of getting gear, so unless there is another mode to play once you've 'maxed out' your gear, then DZ play is going to lose interest very quickly. Also, because gear is tied to level, there's no real incentive to play in the DZ until you're at max level as presumably the PvE will keep you sufficiently stocked until then.
So DZ will become a short-term finale to the game once you're finished with the PvE content, just as it was in the Beta.
(I'm sure you'll have to transit the DZ a few times to get to all the PvE missions, but once you get to a fast-travel point on the far side that won't mean much.)