I like to consume “mass-boutique” collaborations between a mass market player and a boutique player. The mass market player brings the scale to offer lower prices, and the boutique player brings the expertise/aesthetics. For example:

1. Uniqlo U - mass market Uniqlo + boutique Christophe Lemaire
2. Massdrop x Sennheiser HD 6XX - mass market (Mass)Drop + boutique Sennheiser, just don't call it HD 650 for legal/branding reasons

You could even consider private labels a form of mass-boutique collaboration, though I'll write about that another day.