  The CHEERS (CHEmical Enrichment RGS Sample) observations of clusters of
galaxies with XMM-Newton have shown to be valuable to constrain the chemical
evolution of the universe. The soft X-ray spectrum contains lines of the most
abundant metals from N to Ni, which provide relatively accurate abundances that
can be compared to supernova enrichment models. The accuracy of the abundances
is currently limited by systematic uncertainties introduced by the available
instruments and uncertainties in the modeling of the spectra, which are of the
order of 20-30%. We discuss the possible gain of extending the current samples
at low and high redshift. We conclude that expanding the samples would be
expensive in terms of exposure time, but will not yield significantly improved
results, because the current samples already reach the systematic limits. New
instrumentation, like Astro-H2 and ATHENA, and improvements to the atomic
databases are needed to make significant advances in this field.
