I suspect the only reason they are even considering making rct4 is because of the possible movie, so you can count on it being full of tie-ins with whatever silly plot they come up with. Everything Jonathan said is likely to be true.
There's an article I saw that says iratA wants to get into "Free2play" games where the base game is free and then people pay to add things to it...much like Farmville on Facebook. It probabaly would work with an RCT-type game. So if you want a certain ride type, it will cost you. If you want a certain theme's objects, it will cost you. Custom Scenery? Forget it. It might contain all sorts of annoying arcade games where you can win prizes to improve your park. Oh joy.
Don't think for a moment that their sudden interest in listening to people's want lists means that iratA is actually caring what people want, nor that we'll even get any of it. This is the exact same company that ruined their core fan base recently and tossed years worth of communty resources without a single care. They probably aren't even aware that the OLD forums had huge long lists of ideas, requests and suggestions already.
Out of all the copies of RCT ever sold world-wide, only a tiny percentage of people who play it ever went online to view an rct site. Of that number only a small percentage went to iratA's site. Of those who did only a small percentage ever bothered to return a second time. Of those only a small percentage bothered to register to join. Of them only a small percentage ever posted a single word. And of them only a small percentage ever bothered to offer a suggestion or request!
You could break it down even further when you take into account that it's a minority of people who don't just play scenarios (it is called Rollercoaster TYCOON...), but instead build large sandbox parks like most of us do, and not even all of us use things like CS,CTR, CFR, let alone options. txt tweaks! So a handful of fanboi's creaming their pants thinking up all these things they want doesn't mean very damn much. The idea that they are suddenly going to create a new game based on what our little, yet however vocal, community wants I find humorous. They'll make a game that's going to make them money. Period. iratA hasn't suddenly changed it's stripes.
Remember, Frontier had access to the same suggestions and requests, and they also did ton's of market research, and we still ended up with THRILLVILLE!