Just a quick idea that one of my friends made: simultaneous battles.
It would involve multiple small squares/circles/dojos as "mats", spread apart, where in each one, two players would go up against one another. If you are to land outside of the area you were placed in (including another mat) you would be eliminated. It could also function as a ladder; the victorious players would move on to the "next round", where it would continue up until there are two left, where they could fight to the death.
Another idea that I made, derived by the extra people battling at once, is team battles. Team battles, as you'd expect, involves 4+ players, equal amounts on each team, pitting against one another. Once all players on a single team are eliminated, or the time runs out, the team with the remaining players (or more points) would be victorious.
One final idea I have is "multi-battles". It involves 3 - 4 players, all against one another. This one could lead up to great chaos, and, other than the extra players, it would function as a normal battle. It could also be used together with the idea of simultaneous battles and/or team battles.
Been suggested many times, and was actually possible for a while, it however proved really buggy and slow.
Maybe eventually we'll see it but most not some time soon.
I reckon it should only be implemented once the standard of the average PC raises, otherwise some players may not be able to use the feature.
My future self would support this.