Trailer button is present in DialogVideoInfo.xml, like in all other skins (Press "i" keyboard to view info screen).
The idea behind MiniMeedia is to show Fanart, cover and most important info in the views......If you want full info/plot/cast/trailer use the info screen.
But anyway, if you like a trailer button directly in your views create a trailer button in your favourite or all Views, see ViewsCommen.xml and ExtraViews.xml.
In DialogVideoInfo.xml you'll find an example of a trailer button.
You can also create a button on your remote with a function to start trailer.
<onclick>PlayMedia($INFO[ListItem.Trailer])</onclick> when creating a button in skin.
Hmm after some thinking.....It´s not logical to have a trailer button in views because you need to navigate to the button, so it would be for example like the scrollbar (Right scrollbar another right Optionsmenu) So you would create an extra click in your view.
Better can use the info button.
So go for the extra button on your remote to start Item Trailer
List view is the only view with an trailer indicator, maybe I'll add the trailer indicator to all views.
Ops lol forgot it but.... I already did add trailer indicator to the views, only not showcase and wheel view.