When the current pulse flows into a nanostructure its temperature increases due to the Joule heating effect and you have completely ignored this effect while discussing a racetrack memory. My single-pulse measurements on ferromagnetic nanowires suggest that this temperature rise prevents the domain wall motion via STT at room temperature.
Why would the racing tracks have to be vertical? And how will you move data along the length of them? From the way you described it, this sounds more like a high speed transmission solution than a data reading or writing solution. But if you have a better way of explaining what you are on about in terms of SRAM replacement, then I'm all ears.
