I would enjoy something like taming.
Things you could do are:
1) Get monsters to fight for you for a certain period of time and you can get your rope enhanced with gems and enchants to keep them fighting with you longer. (1- goblins 99 - Daganoths?)
2) Tame Monsters to ride on them, (25- horse 75- Dragon 99- Kalphite Queen)
3) Permenently Tame a monster (non members) or 3 (members) To keep in stables (or for Members also in houses)
4) the companion that you permenently keep you can level up, but each has a certain limit, Like the goblin can only go up to about 40 etc.
I made this before summoning came out so I realise theres sort of a resemblance, But it does fit in to everything they said!
Monster taming-combat
New land-could be where you train your companion or learn about the skill (like the summoning and herblore quests)
Pvp- fighting with a monster helps right?

this has been an Idea of mine for a long time
hope you like it, and hopefully JaGeX sees this and considers it if its not the new skill XD