i see you enabled it for article namespace but not page namespace on wikisource,
(need it more at page namespace, where most of the typing occurs / or should occur)
in article namespace the page transclusion works well, (a little far down the menu)
the page header template insertion shifted to wikicode before clicking on pencil icon shifted back to VE; cutting and pasting the previous header template not an option
i was accustomed to having 2 edit tabs, so confused by one, and the need to double click
i was finding it easier to paste headers and pages transclusion in wikicode and then edit in VE; perhaps a VE clipboard / recently used menu would helpful
but stable and not crashing = good first steps
one problem - in chrome trying to add values into page transclusion pop up, it is hard to scroll down, but thrashes up preventing seeing bottom of popup box - hard to tab down to get to fields at bottom this occurs when first trying to add a page and the popup box is at the left; when editing an existing box, then pop-up is in the middle and there is no problem.