I believe the fixtures using the mr-8 lamp were designed for small spaces, low profile where a standard l/v fixture would be visible or out of place.
The mr-8 lamp has always been problematic. Gets very hot, short life, pins easily break, and that was always a hotspot because of the narrow beam patterns. The Jayliter that Gregg mentions here was designed to use a Ushio mr-8 lamp that incorporates a clear lens. No lens built into the fixture..
My question comes from a few requests for Brilliance to offer a mr-8 retrofit lamp. The responses (and lack of) here adequately answer that question.