The tactical choices made in the movement phase in 2nd ed
40k, (and lots of other games,), gave the game its tactical depth.(Along with tactical maneuver into weapons range.)
2nd ed
40k tactical movement choice was **, A)stay still and fire to full effect,B) move and shoot a bit, C)double move and not shoot, D)charge into assault and stop an enemy unit firing at other units.
(**Abbreviated for clarity .)
It was the intention of
GW sales to target a demographic with low tactical focus and a higher ability to just absorb data.(EG targeting children instead of war gamers.)
(According to Rick Priestley and other
GW devs who were there at the time.)
GW plc has steadily removed most tactical considerations from the
40k game play and replaced them with overly complicated strategic choices, and a plethora of exceptions to the core rules,(Special rules.).That contradict or replace the limited core rules.
So people just wanting to push their minatures around a table and throw a few dice to see what happens.Are fine with the
40k game play as it is.
However, I can see lots of people expecting
40k to be an actual war game , finding the rules inadequate for their needs/expectations.
Having all movement in the movement phase has several bonuses, simple tactical choices to improve the depth of game play, much faster game play as minatures only move once per game turn.(And no dice rolling for movement if movement stat returns.)
In my experience using the most straight forward methods to cover the majority of the intended game play, is the best option.The FEW exceptions to this can be covered with special rules.
If I was to include 'pop up attack' in a war game ,I would sinply make the unit declare they were using this special attack at the start of the game turn.The count the unit as 'in cover' rather than 'concealed'.(EG harder to hit rather then than hidden,)