I actually have multiple ideas:

• The possibilty to buy a house/appartment or villa in a city area. Some for premium only and some for free users. They would cost way more then the rooms to rent and you have to pay a daily fee to keep it. If you don't pay in 24 hours you get thrown out and It's available for everyone again. The premium users would have the possibility for a little customizing just like setting a theme. For example romantic/well orginized/medieval/not so well orginized or the sex palace.
  
• The possibilty to have sex in the shower. I know it would be troublesome with the poses :/.
  
• Instead of just having these static phases in the sex scenes it would be cool to let everyone who's face is shown let him choose a face impression just like happy/angry/sexy grin/loosing his/her mind. And some possibilities to "grab" something. For example I'd really like if the guy pulled my hair during a doggy or use my hand during a blow job.
  
• And group sex of course ^-^
  

Sorry if some of these ideas were already posted. I didn't want to read me through 7 pages with each having 50 posts.