I'm new to MRA but I've been working to understand gpx and zumo for a long time. I think I can offer a bit of clarification here.
From a zumo perspective, the key difference between MRA's 1.1 and 1.2 is not that shaping points are eliminated, but that route point extensions are included. They are essentially track points, just formatted and handled differently.
If a route is transferred into the zumo without route point extensions (e.g. MRA's gpx 1.1), it will be calculated based on all available route points, both via and shaping. If the route does include route point extensions (e.g. MRA's gpx 1.2), it will not be recalculated unless the route is subsequently changed.
If a route is fully recalculated by the zumo, the route point extensions are discarded, the route is calculated based on all available route points, both via and shaping. New route point extensions will be generated. Route point extensions are the result of route calculation, never an input to the calculation.
When using CEP, or going off-route with recalculation allowed, the zumo will indicate that it is calculating, but is is not recalculating the entire route. It is only calculating a small route segment. Route point extensions are preserved.
Adding or removing a route point, via or shaping, will result in a full route recalculation, discarding all previous route point extensions. Since MRA's 1.2 discards shaping points, only the via points are available to recalculate the route.
This implies that it would be better to import a route which includes via, shaping, and route point extensions.
I should also note that recent firmware version 6.60 for the zumo XT2 improved off-route recalculation behavior.