Is to v. can be used in a few ways, and does not necessarily state the immediate future— or state the future at all. Directives, for example, can be written this way:
Employees are to wash their hands thoroughly and regularly.
Enforcement is to cease and desist as per the injunction.
As you note, you can express a prediction or expectation of the future in this way, but it is not necessarily the immediate future.
Scientists say Betelgeuse is to explode within the next million years.
In conversational English, it sounds somewhat formal or stilted, and we would more likely say something or someone is going to v. (or planning to, or in Texas fixin' to, or if truly immediate about to or just about to):
I am going to eat liver and onions for supper.
She is not going to kiss me afterwards.
This construction is common in reporting, especially in headlinese:
Seth Myers is to host Late Night after Jimmy Fallon departs for The Tonight Show.
NFL to Add Second Team in Jacksonville