Unfortunately multiplayer is unlikely on the roadmap, but its not completely off the list.
Multiplayer is REALLY hard to implement - There is a lot of fiddly bits to get working just to have client connections (vs the host where it just works like singleplayer) to be able to affect anything. My tests so far with just picking up rocks don't work with multiplayer. I am going to focus on adding more game play elements ( just got enemy catapults mostly working) but if I stumble across the multiplayer solution it may make its way in.