Honestly, nothing… at least for the outnumbered buff itself.
There’s a bunch of posts/drama going around in reddit, discord, and in-game that has to do with the outnumbered buff: namely, the pips it gives and how it is currently encouraging players to do some shady stuff like map hopping at the last moment, tricking others into moving, etc.
Yes, the incentive to go to these outnumbered maps are very high. A 5 pip tick is practically double the amount for most players right now, perhaps even more.
The goal of the outnumbered buff is, quite simply, getting players to go to these maps rather than ignore them so people will help somewhat.
The issue right now, at it’s core, seems to be that its not doing it’s job very well: it does bring people into those maps but they are mostly AFKing, waiting for the tick. They bring the participation in from other maps.
However, on the flipside, making the outnumbered buff not appealing enough to map hop and AFK pip shower is the same as making the outnumbered buff not appealing enough to even look for, period.
The buff should stay as is (thus, do nothing about the outnumbered), but knowing the real core issue the solution is pretty clear:
1) Changing maps or leaving WvW resets your participation.
This shouldn’t be an issue for most people who actually play WvW: you know how fast you can get T6 participation? Pretty quickly, even in small groups, and even quicker in larger zergs.
What this does is grant minor annoyance to those who need to map change, log out, or change characters while making map hopping practically impossible while still keeping the outnumbered buff very appealing.
As a result of this change, in order to make use of the outnumbered buff you basically need to stay somewhat loyal to a map. That is, you need to spend time actually doing things: the map becoming outnumbered should give you an incentive to stay rather than switch maps.
2) Another issue we are having is AFK: not for the outnumbered buff but AFKers in general.
Lowering the AFK timer is, IMO, not a very good solution: some people just need a quick break and it seems like the AFK timer is about 5 minutes. Even still, people have ways of just bypassing the timer by not actually being AFK but rather simply sitting it out for the ticks / WvW reward tracks.
I think the best solution in this case is to give both players what they want: a way to AFK it out and get what you are “owed”, while getting the AFKers out of the maps that could really use the people.
A few days ago, Obsidian Sanctum used to allow this to happen but ArenaNet has since “fixed” it. I think they should change it back and let people know that if you want to use up your ticks for the day just go there, maybe even throw in an extra pip (just 1). In regards to the first suggestion, make switching to Obsidian Sanctum immune to the participation reset, but leaving it will still reset it. Go AFK there where no one gets hurt by it. It’s only really worth it if you are seriously going to AFK all of your participation out as “map hopping” to it and out will set your participation back to 0.
On the topic of WvW suggestions: a leaderboard for most kills, most sentry kills, most yak slapping, etc, would be pretty cool to show, updated every 5 minutes in the WvW tab. No rewards for it (would encourage some abuse) but would be really fun to have.
TL;DR: reset participation on map change/leave except when ONLY entering obsidian sanctum to push all the AFKers to AFK there.