The replaygain tag value is the r128 Integrated value, at least if you use foobar. Foobar writes the sample peak rather than true peak, but the two values are within a fraction of a dB of each other, so the difference isn't relevant.
If you want the last few hundred milliseconds loudness on the wps, that'd have to require more significant changes to the wps. The peak meter does something similar although without the weighting. That might be a starting point.