Sounds like a *fantastic* item to contribute to the firmware revision thread! There's no reason a simple ping-pong delay can't be built in. On the EHX Cathedral reverb pedal, there's a setting that turns it into a simple digital delay. In mono, it's a mono delay. But if you run both outputs, it automatically switches to a basic left-right-left-right ping-pong setting.
It would NOT be hard to program either that or a selectable-in-menu setting to enable ping-pong for stereo, on a by-preset basis.