This seems unnecessarily terse. If you want types, why not make it look like one of the existing popular languages with types? (Rust/TypeScript/protobuf)

Instead of:

    uxf 1
    =Database server:str ports:list connection_max:int enabled:bool
    =DateTime when:datetime tz:str
    =Owner name:str dob:DateTime
    =Hosts name:str
    [
      (Owner <Tom Preston-Werner> (DateTime 1979-05-27T07:32:00 <-08:00>))
      (Database <192.168.1.1> [8000 8001 8002] 5000 yes)
      (Hosts
        <alpha>
        <omega>)
    ]

Why not:

    type Database {
      server: str,
      ports: list,
      connection_max: int,
      enabled: bool,
    }
    type DateTime {
      when: datetime,
      tz: str,
    }
    type Owner {
      name: str,
      dob: DateTime,
    }
    type Hosts {
      name: str,
    }

    [
      Owner('Tom Preston-Werner', DateTime('1979-05-27T07:32:00', '-08:00')),
      Database('192.168.1.1', [8000, 8001, 8002], 5000, yes),
      [
        Hosts('alpha'),
        Hosts('omega'),
      ],
    ]

Evidence shows that people like that kind of format, for "plain text human readable" purposes. They are also used to it. It's only 20% longer, and you can also go with a Haskell-style syntax if you dislike braces.

What's the point of a plain-text format that is not human-friendly? Especially for type definitions, do you expect people to write this or do you want them to compile their schema from a different human-readable format into your human readable-format (and why)?