Heads up (yes, I know, not yet supported). Testing on staging site with current version of X + 4.9.6 + WC3.4RC-1.
Customizer does not work (does not save + small error message that something went wrong, try again later).
Console errors:
Failed to load resource: the server responded with a status of 500 ()
/en/shop/?customize_changeset_uuid=c991cacb-124b-4c76-a566-6a7b4c96299c&customize_theme=x-child&customize_messenger_channel=preview-1:1 Failed to load resource: the server responded with a status of 500 ()
/wp-admin/admin-ajax.php:1 Failed to load resource: the server responded with a status of 500 ()
/en/checkout/?customize_changeset_uuid=c991cacb-124b-4c76-a566-6a7b4c96299c&customize_theme=x-child&customize_messenger_channel=preview-2:1 Failed to load resource: the server responded with a status of 500 ()
/en/checkout/?customize_changeset_uuid=c991cacb-124b-4c76-a566-6a7b4c96299c&customize_theme=x-child&customize_messenger_channel=preview-3&customize_autosaved=on:1 Failed to load resource: the server responded with a status of 500 ()
test.demo.site/:1 Failed to load resource: the server responded with a status of 500 ()
7/wp-admin/admin-ajax.php:1 Failed to load resource: the server responded with a status of 500 ()
test.demo.site/:1 Failed to load resource: the server responded with a status of 500 ()
9/wp-admin/admin-ajax.php:1 Failed to load resource: the server responded with a status of 500 ()
load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4 POST https://test.demo.site/wp-admin/admin-ajax.php 500 ()
send @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4
ajax @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4
(anonymous) @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:17
a.Deferred @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:9
send @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:17
post @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:17
f.requestChangesetUpdate @ load-scripts.php?c=0&load[]=heartbeat,customize-base,customize-controls,customize-widgets,jquery-ui-position,wp-pointer,jquery-ui-resizable,jquery-ui-button&load[]=,jquery-ui-dialog,wpdialogs,jquery-ui-slider,jquery-touch-punch,iris,wp-color-picker,suggest,accordion,customize-nav-menus,mce-v&load[]=iew,imgareaselect,image-edit,customize-models,customize-views,updates,quicktags,wplink,jquery-ui-menu,jquery-ui-autocomplete,thi&load[]=ckbox,media-upload&ver=4.9.6:3
e @ load-scripts.php?c=0&load[]=heartbeat,customize-base,customize-controls,customize-widgets,jquery-ui-position,wp-pointer,jquery-ui-resizable,jquery-ui-button&load[]=,jquery-ui-dialog,wpdialogs,jquery-ui-slider,jquery-touch-punch,iris,wp-color-picker,suggest,accordion,customize-nav-menus,mce-v&load[]=iew,imgareaselect,image-edit,customize-models,customize-views,updates,quicktags,wplink,jquery-ui-menu,jquery-ui-autocomplete,thi&load[]=ckbox,media-upload&ver=4.9.6:5
(anonymous) @ load-scripts.php?c=0&load[]=heartbeat,customize-base,customize-controls,customize-widgets,jquery-ui-position,wp-pointer,jquery-ui-resizable,jquery-ui-button&load[]=,jquery-ui-dialog,wpdialogs,jquery-ui-slider,jquery-touch-punch,iris,wp-color-picker,suggest,accordion,customize-nav-menus,mce-v&load[]=iew,imgareaselect,image-edit,customize-models,customize-views,updates,quicktags,wplink,jquery-ui-menu,jquery-ui-autocomplete,thi&load[]=ckbox,media-upload&ver=4.9.6:5
load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4 POST https://test.demo.site/wp-admin/admin-ajax.php 500 ()
send @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4
ajax @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,underscore,wp-a11y,wp-util,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,jquery-&load[]=ui-draggable,jquery-ui-droppable,backbone,wp-backbone,wp-ajax-response,jquery-color,wp-lists,postbox,nav-menu,wp-codemirror&ver=4.9.6:4
j @ load-scripts.php?c=0&load[]=heartbeat,customize-base,customize-controls,customize-widgets,jquery-ui-position,wp-pointer,jquery-ui-resizable,jquery-ui-button&load[]=,jquery-ui-dialog,wpdialogs,jquery-ui-slider,jquery-touch-punch,iris,wp-color-picker,suggest,accordion,customize-nav-menus,mce-v&load[]=iew,imgareaselect,image-edit,customize-models,customize-views,updates,quicktags,wplink,jquery-ui-menu,jquery-ui-autocomplete,thi&load[]=ckbox,media-upload&ver=4.9.6:1
(anonymous) @ load-scripts.php?c=0&load[]=heartbeat,customize-base,customize-controls,customize-widgets,jquery-ui-position,wp-pointer,jquery-ui-resizable,jquery-ui-button&load[]=,jquery-ui-dialog,wpdialogs,jquery-ui-slider,jquery-touch-punch,iris,wp-color-picker,suggest,accordion,customize-nav-menus,mce-v&load[]=iew,imgareaselect,image-edit,customize-models,customize-views,updates,quicktags,wplink,jquery-ui-menu,jquery-ui-autocomplete,thi&load[]=ckbox,media-upload&ver=4.9.6:1