Well, trying not to be too biased towards f2pers here...
1) Allow f2pers to craft Chaos Runes. The temple's in an f2p place (correct me if I'm wrong - I've never been a member), so why not let us make them?
2) Ban any proven hackers/scammers/autoers
3) Create an official RS secret Police (headed by me

), dedicated to doing 2)
4) More updates for higher lvl players
5) Committed, nice f2pers who help people with quests *cough*like I did last night*cough*, don't scam, and are generally nice are rewarded with a one/two month free membership, which they can then opt to continue paying after it runs out.
That's all I can think of off the top of my head...
Ciao,
Forgotmytea