  Spectrally and spatially varying ensembles of emitters embedded into
waveguides are ever-present in both well-established and emerging technologies.
If control of collective excitations can be attained, a plethora of coherent
quantum dynamics and applications may be realized on-chip in the scalable
paradigm of waveguide quantum electrodynamics (WQED).Here, we investigate
inhomogeneously broadened ensembles embedded with subwavelength spatial extent
into waveguides employed as single effective and coherent emitters. We develop
a method permitting the approximate analysis and simulation of such mesoscopic
systems featuring many emitters, and show how collective resonances are
observable within the waveguide transmission spectrum once their linewidth
exceeds the inhomogeneous line. In particular, this allows for near-unity and
tailorable non-Lorentzian extinction of waveguide photons overcoming large
inhomogeneous broadening present in current state-of-the-art. As a particular
illustration possible in such existing experiments, we consider the classic
emulation of the cavity QED (CQED) paradigm here using ensembles of rare-earth
ions as coherent mirrors and qubits and demonstrate the possibility of strong
coupling given existing restrictions on inhomogeneous broadening and ensemble
spatial extent. This work introduces coherent ensemble dynamics in the
solid-state to WQED and extends the realm to spectrally tailorable emitters.
