Renoise already have Track Scope and Master Scope.
An idea is to have a Waveform Scope where you can see the output signal like a wav file.
The waveform signal can be streamed horizontal from right to left.
There’s a hidden option in the Config.xml (click on “Help” -> “Show the Preferences folder”, open Config.xml in a text editor) to set the scope window width in samples. -> “TrackScopeWidthInSamples” If you set it to a bigger amount like 4096 and disable "TrackScopeSnapToZero"you will get a moreWaveform alike display. It does not scroll though. Could add some easy configuration in the UI for this if it’s useful.
Here is a great freeware scope you can use beside Renoise, great if you have two monitors. It has three different monitors, xy graph (phase view), oscilloscope and frequency view. You can adjust speed, amplitude, log/lin curves, hold time for the phase view and so on. Works with all my audio drivers.