  In the quest for the faint primordial B-mode polarization of the Cosmic
Microwave Background, three are the key requirements for any present or future
experiment: an utmost sensitivity, excellent control over instrumental
systematic effects and over Galactic foreground contamination. Bolometric
Interferometry (BI) is a novel technique that matches them all by combining the
sensitivity of bolometric detectors, the control of instrumental systematics
from interferometry and a software-based, tunable, in-band spectral resolution
due to its ability to perform band-splitting during data analysis (spectral
imaging). In this paper, we investigate how the spectral imaging capability of
BI can help in detecting residual contamination in case an over-simplified
model of foreground emission is assumed in the analysis. To mimic this
situation, we focus on the next generation of ground-based CMB experiment,
CMB-S4, and compare its anticipated sensitivities, frequency and sky coverage
with a hypothetical version of the same experiment based on BI, CMB-S4/BI,
assuming that line-of-sight (LOS) frequency decorrelation is present in dust
emission but is not accounted for during component separation. We show results
from a Monte-Carlo analysis based on a parametric component separation method
(FGBuster), highlighting how BI has the potential to diagnose the presence of
foreground residuals in estimates of the tensor-to-scalar ratio $r$ in the case
of unaccounted Galactic dust LOS frequency decorrelation.
