This feature has been requested before, here:
I too wanted several x-axis to be linked. Presently, I have a workaround which uses relayoutData server-side. Interaction with graphs it not great - because there is a slight delay when zooming in one graph before the scale on other graphs changes. But it does work!
Now that custom Clientside javascript can be run it should be possible to do this a bit better.
My implementation uses python, so would have to add a bit of JS in as well - but not too much of an issue.