At present, shadow servers leave the keymap completely untouched and try their best to find a matching keycode when we receive a key event from the client (see ticket:2301#comment:35). We could add the option of re-configuring the shadow server's keymap to have the keys the client is likely to need.
ie: with a shadow server configured with 'us' layout and a client connecting with a 'gr' layout could use a 'us, gr' layout and make all the keys accessible.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2630