  We present forecasts on the primordial non-Gaussianity parameter
$f_\text{NL}$ of feature models for the future Cosmic Microwave Background
Stage-4 (CMB-S4) experiments. The Fisher matrix of the bispectrum estimator was
computed using noise covariances expected for preliminary CMB-S4 specifications
including ones for the Simons Observatory. We introduce a novel method that
improves the computation by orthonormalising the covariance matrix. The most
sensitive CMB-S4 experiment with 1' beam and 1$\mu K$-arcmin noise would yield
a factor of 1.7-2.2 times more stringent constraints compared to Planck. Under
the Simons Observatory baseline conditions the improvement would be about
1.3-1.6 times to Planck. We also thoroughly studied the effects of various
model and experimental parameters on the forecast. Detailed analysis on the
constraints coming from temperature and E-mode polarisation, in particular,
provided some insight into detecting oscillatory features in the CMB
bispectrum.
