This should work:

from typing import *

T = TypeVar('T')  # Any type.
ValueOrCallable = Union[T, Callable[..., T]]

class Foo(object):
  state:  ClassVar[ValueOrCallable]

I don't know of an easy way to make the type definition itself parameterisable without making it a class unto itself.

But perhaps this is close enough to what you want:

from typing import TypeVar


class MyClass:
    pass


# instead of defining a parameterisable type, why not define the types you need?
MyType = TypeVar('MyType', MyClass, str, None)


def fun(x: MyType):
    if isinstance(x, MyClass):
        print('MyClass', x)
    elif isinstance(x, str):
        print('str', x)
    elif x is None:
        print('None')
    else:
        print('Something unexpected was passed')


fun(MyClass())
fun('test')
fun(None)
fun(1)

Output:

MyClass <__main__.MyClass object at 0x0000028D566CEA10>
str test
None
Something unexpected was passed

And in editors that check for it (for example in my case PyCharm), you get a warning like "Expected type 'MyType', got 'int' instead" on the last line fun(1), specifically on the 1.

Note: from the comments you've made it clear this is not ideal for you, but I'll leave the answer up for others looking and deciding it does work for them.