Inspired by this thread (You're in for a big surprise.), where Thomas Tompion gave the definition of "to be in for something", I was wondering if changing the tense would make the set expression sound strange. Is it the fact that the future sense has already been signaled in "to be in for something" that there's no need to say "you'll be in for a big surprise"? Eg.) If you think I won't gut you myself to get that key, you'll be in for a big surprise.