and then observe closely to see if the 2yr rotation continues to be so fiercely defended, or whether, instead, it begins to be seen as more embuggerance than
It's already seen as an embuggrance. Most would like more stability I think, even if the moves do pay the fees. I'm not sure if that feeling extends to the VSOs that make the decisions of course...
The problem is the current career model doesn't work without frequent moves and even when/if the model finally improves, some officers will still need to move around fairly often even if not quite every two years. There are intractable problems like the need to fill jobs at dispersed units, and sites that aren't near the rest of the army like MOD main building.