Board Thread:Support Requests - Designing Your Wiki/@comment-10569546-20130609214512/@comment-452-20130609220127

MediaWiki:Createpage-with-video. It used to be MediaWiki:Newarticletext, but was changed recently.

See also: Extension:CreateBox, which shows you how to easily include other preload layouts when creating a page from a create box.

You can also add &preload=Template:MyLayoutTemplate to the end of any edit url.

You can use MediaWiki:Newarticletext to add a message to the top of the editor when editing pages which don't exist, with links to preload different layouts.

edit: and one other thing, since you mentioned visiting pages which don't exist, you may also like to edit Mediawiki:noarticletext, which is the default text shown when pages don't exist - that would also be a convenient place to place links which will preload a layout, instead of the standard "Add to this page" link.