There is a very good onionshare it will work in Whonix 14. But it will require a little user command line action.
Should we install onionshare by default?
The usability issue will be, that onionshare will not out of the box. We really shouldn't enable the control-port-filter-python config for onionshare by default, as it enables the workstation to set up Tor hidden services. (And Tor with hidden services is less secure than Tor as client only.)
onionshare in these cases currently fails in a usability wise very bad way. The gui keeps stuck in "Starting the onionservice...". (Posted an onionshare feature request to improve the error handling. - But it most likely won't make it into Debian version 9 codename Stretch.)
Our options are having it only available in Whonix onionshare documentation or installing it by default on still requiring a user to read and apply the Whonix onionshare documentation.
For Whonix releases later than Whonix 14, this could be improved usability wise. Most conveniently in Qubes-Whonix there could be on onionshare launch a qrexec call where then a gateway gui explains this and lets the user enable or not enable the required onionshare config.