While it may not be possible to run an SMB server without root, it is possible to run a WebDAV server without root for a similar effect.
Setting up an Android WebDAV server
On my stock Nexus 7, I installed WebDAV Server, opened it, clicked on the start button and was immediately able to see my
/storage/sdcard folder in my web browser at the URL displayed by the application, i.e.
Note that with WebDAV, you also have the option of selecting Root (/) or DCIM as well as SdCard as the WebDAV root.
Using the WebDAV server through Windows Explorer
I then mapped
http://192.168.x.y:8080 as a network drive in Windows Explorer and could the access the contents of my storage drive, just as if I was connected via MTP, but through a drive letter.
Sadly, this solution is incredibly slow.
Every directory change takes between 6 and 20 seconds, as does accessing most files. Once a file is accessed though, it transfers at a reasonable speed (copying a single 42MB file in Windows Explorer took around 60 seconds, so 700KB/s).
Thus WebDAV via Windows Explorer is Ok for downloading a few large files whose location you know, but browsing or syncing a whole device this way isn't quick. I synced 1.75GB of data in around 6000 files and 400 directories and it took 10 hours, i.e. around 50KB/s or 10 files/dirs per minute on average.
Using the WebDAV server through Windows command line
Even from the command line, each directory listing takes 5-6 seconds, as does any file access. Copying the same 42MB file from the command line took around 20 seconds, so around 2.1MB/s.
Using the WebDAV server through a web browser
The fastest option for WebDAV is to use your web browser though, directly through the URL given. Changing directory rarely takes more than a second and downloading the same 42MB file from the command line took around 12 seconds, so around 3.6MB/s.
The downside of using the web browser is that it only shows the date (no size or type) and makes no distinction between files and directories so if a file doesn't have an extension (or a directory does) then it may not be obvious if clicking on a link will take you to another web page (for a directory) or start a download (for a file).
By default, Windows limits the size of WebDAV downloads to 50000000 bytes (47.6MB), though this can be changed through a registry hack (
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WebClient\Parameters) if you know what you are doing.
WebDAV access is not secure. Even if you set a password on the WebDAV share, the connection is still
https, so it is not encrypted. Only use WebDAV on a secure wifi network and certainly don't enable the WebDAV server while you are in an internet cafe or other unsecured wifi.