To end proposals for new syntax to do what they do for triple-quoted strings. Nick Coghlan gave reasons as follows: run time cost small, can be optimized away, would be used more than some other string methods. 
http://mail.python.org/pipermail/python-ideas/2013-July/021717.html

In response, Guido said "That's a compelling argument. Let's do it."
http://mail.python.org/pipermail/python-ideas/2013-July/021718.html

It turns out there's one slight wrinkle in this grand plan: it won't work for docstrings without some additional tweaking to allow for method calls in the docstring detection.

>>> def f():
...     """example""".lower()
... 
>>> print(f.__doc__)
None
>>> import dis
>>> dis.dis(f)
  2           0 LOAD_CONST               1 ('example') 
              3 LOAD_ATTR                0 (lower) 
              6 CALL_FUNCTION            0 (0 positional, 0 keyword pair) 
              9 POP_TOP              
             10 LOAD_CONST               0 (None) 
             13 RETURN_VALUE

I still think the methods are worth adding regardless - I just anticipate a request to allow method calls on docstrings to follow not long after ;)

str already have too many methods. Who uses str.swapcase() or str.zfill() now? I'm -0.5 for adding any new str methods.

.dedent() is a no-brainer.  JFDI.  +1

.indent() I guess makes sense for symmetry, although I've rarely used it.  -0

As for docstrings, I can imagine other alternatives, so let's let someone interested in that go through the PEP process.

IMO it’s fine that docstrings continue to live as pure string literals, and documentation tools continue to follow PEP 257’s advice.

If this goes ahead, would a bytes.dedent() method be also considered? I recently discovered that textwrap.dedent() does not work on bytes() in Python 3. I would have used it for the contents of an input file in a test case.

For the record there’s an older issue 1237680 on this, rejected in 2005.