I like the “Welcome to Discourse Meta!” banner on the frontpage of this platform. How can this be configured? Would like to have that on my discourse instance, too 
「いいね！」 1
Maybe by using this theme component: Versatile Banner
「いいね！」 2
Do you know if that can be used in hosted discourse?
「いいね！」 1
That’s right, that is the theme component used here as it is easy to customise. Adding on to this, this according to Kris it is likely that they will make it fully configurable and share it here on meta.
@simon.dueckert see this
You can install this TC on a hosted site 
「いいね！」 2
I’ve made a configurable version of the banner available here:
「いいね！」 3