During a real world visit to Jagex's office a few years ago, my clanmates and I were told definitively that "the forums are not a priority" for Jagex. That hasn't changed.
They're not going to invest time and money in resurrecting them until they finally realise that they're currently captive to the whims of people of Elon Musk and the bearpit that is Reddit.
As to incentives... there already is one, at least: the coloured metal/gem button you can see when you hover over a poster's name.
~~~~ Just another victim of the ambient morality ~~~~
Throughout the years, we have all been advocating for more activity here on the Forums, both from Jagex themselves and members of the community. Unfortunately, with Social Media running rampant, it became easier for everyone -- specially Jagex Moderators outside of HQ -- to engage with the community without limits. It's really hard for the Forums to compete with Social Media.
With that being said, as Archaeox mentioned above, the Forums aren't a priority to Jagex. To read more on that, you may rely on Mod Lyon's response below:
Thanks so much for the suggestions. Some new and not so new suggestions there.
I think there are some we're more likely to think about than others, I don't feel the "active users now" is accurate and just leads to some of our users misunderstanding because of it, for example so we'd leave any further activity monitor our of updates and frankly probably get rid of the existing one. It doesn't add much value.
Notifications on the other hand, definitely a must have from the community minded JMods if we had free reign over these updates.
Like Mrs Ana shared,
the forums aren't [regrettably] our current priority
, and we're working hard on some big development sized work at the moment. I'll keep your thread on our community suggestions notes though and relay this to the rest of the team, if we manage to get round to updating these hallowed halls.