Design looks great. Most of my comments are about consistency in docs and some logic flows.

Realizing it's kind of weird that we've been doing this based on path name length, and not number of directory components. Should we revisit that?
Right now, this:

/src/oh-boy-this-repository-name-is-long`


is considered deeper than:

/src/repos/libfoo/src

While here, can we change these to logging.warning?

"Return ..."

We can just return None at the end.
Could even merge in the client_root check above with the client_root.lower() check, and simplify it all further.

We can skip the else: here, just return None.

Since this is the Subversion code, we can probably make these docs more specific to Subversion's behavior.

No need for parens.

We can skip the else: and just return None.

Totally your call here, but since we're almost certainly going to hvae a result from this call, if info is set, we can skip the extra checks and do:

try:
    path = info['Repository Root']
    ...
except KeyError:
    return None

Is this here so that Git and Mercurial can get access to it?
Given how similar the name is to the SCMClient version, maybe we should rename it. I was pretty confused for a second.

Can you add a blank line between these?
Any reason we can't import this at the top of the file?

No need for the else:.

We have a few versions of the docstring for this function. Let's copy/paste one summary for all of these, at least, so they don't diverge further down the road.

No need for the else:.

No need for the else:.

No need for the else:.

No need for the else:.

Why the direct comparison? Is None a valid option?

Can you add Version Added?

Can you add Version Added?

There's a danger with this line (and any like it). One of the warts of Python.


>>> d = {}
>>> print(d and 'key' in d)
{}
>>> n = None
>>> print(n and 'key' in n)
None


Due to the old-style ternary-ish statements Python allowed, we have to be very careful to explicitly compare each part of this if we're going to return it as a boolean. So, info is not None or bool(info) or whatever makes sense here.
I know we've done this wrong in places, and while it normally isn't an issue, I have fixed an obscure bug or two in the past due to this sort of quirk.
This might apply to other parts of the code. I haven't gone through carefully, just noticed this here.

This could be:

local_path = info.get('Working  Copy Root Path')

Can this use the new deprecated class?

These still have to go before Returns, in order to render correctly.

Same here.