Back in the day, a studio called Frontier Developments worked on RollerCoaster Tycoon 3. Since then they went on to work on a number of titles including Screamride for the Xbox and now Planet Coaster for the PC. This is perhaps everyone's best bet when it comes to a spiritual successor to RCT3, because there are probably no other developers more qualified to give that to you than the people who actually made RCT3.

There are a bunch of pre-order options for you to take a look at. Pre-order prices start around $30 (USD).