Our team, lead by Yuken Ohshiro (ISAS/JAXA), has developed an optically-thin thermal plasma model which calculates non-equilibrium temperature and ionization processes. The ApJ paper has been published (ADS). This is an updated version of the conventional XSPEC models (nei, rnei), where the electron temperature is assumed to be constant in time.
New non-equilibrium thermal plasma model
Astrophysical Research Works of Hiromasa Suzuki 