Maybe for the rest of this year we get free add on items like we have been getting so far,with maybe some spooky items for Halloween and another update for Christmas. As far as any expansion packs are concerned, I don't think we will get these until the spring of 2018 (maybe a Water Park pack) which won't be free. I don't think we will get any more free updates of any size after this year, except patches to improve game play or fix bugs. I think that next year, Frontier will be concentrating on a new game, but will continue to make more DLCs that will add more themes, animatronics , such as a Dinosaur pack or maybe some scifi stuff.
As far as new coasters and flat rides, I think these will come in paid for expansion packs, like there was for RCT3. I think for what Frontier has given us so far for free, is pretty outstanding, but they can't carry on giving free update packs for much longer. This is just my personal opinion, but I think Frontier will wind down with free stuff after this year and just concentrate on some more DLCs and maybe a couple of larger expansion packs.