Good question! One of the key aspects (which you pointed out) about training for Nordic at higher altitudes is building and maintaining speed. You’re limited in how much sustained (extensive) high-intensity work you can do, so therefore in order to maximize specific speed training I’d recommend short repeats at very high rates, just as you were thinking. Start with even just 10-15sec sprints with long, easy rest (2-3min easy skiing or even standing) where you really focus on good technique at the highest rate possible. Then move up to 30-60sec max as your “interval” duration. For these I would still maintain a decent rest interval of 1-2 minutes to begin. As your speed gets better you can move to something like a 30-30 interval session but pay close attention to maintaining that speed output; if it starts to really drop off, then bag the intervals and just ski aerobically.
You will have innate advantage racing at lower altitudes, which will somewhat compensate for not doing as much volume of extensive high aerobic (Zone 3, Zone 4) workouts. Doing these lower-elevation races themselves will also serve as valuable training of those higher zones. And by working on pure speed and efficient technique at that speed while at high elevation, you’ll further maximize the aerobic efficiency you have and make the best use of your well-acclimated system.