You don't need the fully bloated sftp for transferring files and such, you can use "scp" (and its windows version) on the built-in dropbear ssh implementation.
Indeed You do not need the full openssh.
The only thing You do need in order to work with nautilus ,gftp or fillezilla as client. Is the sftp-server module which is so small as 28 bytes.
For the rest it's just using the dropbear ssh from openpli. like is done for scp.
For windows yes that's a case apart, windows self does not support sftp standard like does nautilus from ubuntu. Then You can use scp .
But If You install Filezilla in windows it does work ass well.
It's all a mather of choice, what the users prefer. The most of ubuntu users do like the use off nautilus which is a very good file browser.
Also I really like Gftp on linux as there we can even set options to keep and or change file rights , And gftp is really booming, the performance is amazing with it. especially for large video files. On Gb network the performance limitation is not the network anymore but the pc's busses and drives self.
Note with openpli 4.0 , the openpli oe core does not install the sftp-server(module) into /usr/libexec anymore but in /usr/lib/openssh .
As far as I looked up on the net, that module must be in /usr/libexec .
Anyway, As test I once give it a try by installing the full openssh to my box dm8000 running openpli 4.0 . i did not worked out.
Which lead me to think that's it is actually a bug into oe core.
As a work around i just modified the specifig openssh-sftp-server module package by adding a pkg_postinst for that package into the bb file concerned. Which just creates the /usr/libexec directory (if it did not existed already) and then creates a link to the /usr/lib/openssh/sftp-server module into that folder.
Then its' booming again.