I will briefly introduce the fundamental limitations of modern mid-IR facilities, both from ground and in space, and highlight their unique discovery spaces. I will generally discuss the unique challenges that ELTs impose on mid-IR instruments, from adaptive optics and high-contrast imaging to the complex thermal infrared background and and alternatives to classical chopping/nodding techniques. I will use the specific examples of the planned ELT instruments METIS (ELT) and MICHI (TMT) to illustrate how these challenges impact their conceptual design and capabilities.