Battle Royale is a fun minigame with some great rewards that require many games to complete, I fully support these suggestions as it can be near impossible to get consecutive games of BR going due to the fact that nobody wants to wait.
My personal input would be this:
Scattered Loot:
Instead of offering the likes of Green D'hide, Leather and other low tier items, start at a 45 Defence and above setup (as the unlucky gear). Include miscellaneous Barrows as more common gear, alternative weapons (SoL, Crossbows, Whips) with chest loot being pushed towards tier 65 gear (Barrows, Armadyl, special weapons etc).
End Zone:
The end zone is what is the issue with BR. People will run around consistently refilling their food supply with the shop or ladder hopping between floors to avoid being hit. While disabling the ladders in the end zone may be a bit more difficult to achieve, force the zone to shrink until it is a 2x2 square to force the last contenders to fight (size could vary). Alongside forcing them to fight, disable the shop in the final zone to avoid people consistently refilling their food supply; dragging these games out for a considerable time.