Mind the bloat if you do not want to sink the boat.
I did find this however, which goes into details about why Ember was not a good choice for them: http://discuss.flarum.org/139-introducing-flarum-s-fast-new-...
Seems to be a well based choice. Doesn't seem to have anything to do with performance though.
While Mithril is probably a lot more extensible and easeier to work with since there's a smaller API surface, seeing "templates" like this makes me sad:
view() {
return m('div.text-editor', {config: this.element}, [
m('textarea.form-control.flexible-height', {
config: this.configTextarea.bind(this),
oninput: m.withAttr('value', this.oninput.bind(this)),
placeholder: this.props.placeholder || '',
disabled: !!this.props.disabled,
value: this.value()
}),
m('ul.text-editor-controls', listItems(this.controlItems(). toArray()))
]);
} {
"jsxPragma": "m"
}