There is a lot of debate going on about UGC at the moment and understandably, a lot of people want it.
As far as I am concerned I will be quite happy to play the game as it is on release, there will be plenty of scenery to keep me happy for quite a while, designing my parks, as well as plenty of managing ready made scenarios like there was when RCT3 was first released.
Over the next couple of years, we had the two expansion packs, Soaked & Wild, which gave lots more rides, scenery items, themes and so on, which enable even better parks to be created. It wasn't until the community started making UGC, that lots more scenery packs became available to download and install into your game, to make even more spectacular buildings and themes including dark ride theme packs and so on.
This was all well and good, but there was no proper control when it came to UGC, because Atari at that time, only hosted a Coaster, Scenario & Park Exchange site where you could download coasters and parks that other people had created. So all UGC had to be uploaded to user websites or file share hosting sites, where they could be downloaded and then installed into your game. The trouble was, there was no proper control over any of this UGC. Most of it was good, other stuff was full of bugs and you took your chance after downloading it, that it wouldn't corrupt your game after installing it.
Some of these UGC files were made very well, with exe installation, so it put everything into the correct file folders in your game. Some UGC files, had to be manually inserted in to the game folders, often with no read me file attached, explaining which folders you had to insert the different files types. So unless you knew how to deal with files, and where to put them, there was every chance your game would not run those files. Then there was the file extension issue. Some files needed Winzip, others 7z and some Winrar for them to be opened.
This is why I would like to see UGC hosted by Frontier or Steam Workshop, or whatever, where they can be checked properly for any virus or bugs before installing and then for the installation to be automatically installed correctly into the proper folders into your game.
But even if UGC doesn't get accepted, for a few years, we will have enough to keep us amused, because I am sure frontier will give us plenty of new content in the way of expansion packs, similar to those we had for RCT3. Yes UGC is great, but it needs to be hosted properly in one place, where it can be verified and checked, not just uploaded willy nilly to any website/file sharing site that you find, then in twelve months time, that website has closed down or disappeared into the ether.
I still play RCT3 and have lots of UGC and I have downloaded quite a few really good parks, that need certain UGC to work. So you try to find that content and find that the site it is available from, has either deleted the file, or they no longer hosts it, so that really, that brilliant park you fancied downloading, is useless to play, because you cant get hold of the content, needed to run it.