Syncing iMessage and webOS Messages is now possible, thanks to some open source bits...
Message Bridge runs on a Mac with iMessage on it, and makes your messages available via REST on your home network:
https://github.com/dremin/message-bridge
And the first new Synergy connector for webOS in a decade (maybe more?) syncs messages into your Messaging app:
https://github.com/webOSArchive/webos-imessage-synergy
Drop me a line if you want to try it out. It works on Touchpads for now, and is currently "read only" -- both limitations should be fixable in the future.