Just remove the ∈ and ⟨ characters, and make braces mandatory:

  for i 0:N:5 {
    // loop body
  }

By the way, the same should have been done with if and while: optional parentheses, mandatory braces:

  if a == b {
    // code
  }

  while idx < end {
    // code
  }

It's possible that parsing a complex condition wrapped by parentheses was found more convenient.

It’s not. Not for humans (the extra parenthesis is just useless clutter), and not for machines (I’ve written parsers, both alternatives are as easy to implement).