The Reichsschutz would similar to the BA Sanguinary Guard, right?
I thought of the renamed Reiksguard as a small-scale Deathwatch. The Reichsschutz members not only protect the Chapter Master, they serve as a reserve with which he can instantly exploit openings other Companies tear in the enemy's defenses. In addition, by drawing its members from other Companies, the Reichsschutz
1) Encourages various Companies' Marines to cooperate, minimizing potentially disastrous rivalries; as well as preparing them for the day they must fight alongside each other when a threat demands the Chapter meet it with multiple Companies, if not all 1000 Marines.
2) Encourage the Marines to be loyal to Malleus and the Chapter as a whole, instead of just to their home provinces and their Companies. This helps prevent the Captains from usurping the Chapter Master's authority; or doing what the Elector-Counts did to each other in Warhammer Fantasy
, and waging wars to increase their own province's size at the expense of another Elector-Count.
Also, the "State Troops" of the Empire could easily be represented on the tabletop as Astra Militarum regiments, with the more elite Knightly Orders being the Space Marines.
Good idea. The "count as Astra Militarum regiments" likely have Chapter serfs in leadership positions, to maximize the Chapter's control over the planet. (I doubt any Space Marine leader will be happy if he returns from a battle on a distant planet, to find some unaugmented human overthrew his authority over the Chapter planet.)