We estimate the detectability of X-ray metal-line emission from the circumgalactic medium (CGM) of galaxies over a large halo mass range ($mathrm{M}_{mathrm{200c}} =10^{11.5}$-$10^{14.5},mathrm{M}_{odot}$) using the EAGLE simulations. With the XRISM Resolve instrument, a few bright (K-$alpha$ or Fe L-shell) lines from $mathrm{M}_{mathrm{200c}} gtrsim 10^{13},mathrm{M}_{odot}$ haloes should be detectable. Using the Athena X-IFU or the Lynx Main Array, emission lines (especially from O$,$VII and O$,$VIII) from the inner CGM of $mathrm{M}_{mathrm{200c}} gtrsim10^{12.5},mathrm{M}_{odot}$ haloes become detectable, and intragroup and intracluster gas will be detectable out to the virial radius. With the Lynx Ultra-high Resolution Array, the inner CGM of haloes hosting $mathrm{L}_{*}$ galaxies is accessible. These estimates do assume long exposure times ($sim 1,$Ms) and large spatial bins ($sim1$-$10,mathrm{arcmin}^{2}$). We also investigate the properties of the gas producing this emission. CGM emission is dominated by collisionally ionized (CI) gas, and tends to come from halo centres. The gas is typically close to the maximum emissivity temperature for CI gas ($mathrm{T}_mathrm{peak}$), and denser and more metal-rich than the bulk of the CGM at a given distance from the central galaxy. However, for the K-$alpha$ lines, emission can come from hotter gas in haloes where the virialized, volume-filling gas is hotter than $mathrm{T}_mathrm{peak}$. Trends of emission with halo mass can largely be explained by differences in virial temperature. Differences between lines generally result from the different behaviour of the emissivity as a function of temperature of the K-$alpha$, He-$alpha$-like, and Fe~L-shell lines. We conclude that upcoming X-ray missions will open up a new window onto the hot CGM.
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