Let Queen count as 2 points and rook as 1. Chess endgame has begun when both players have 2 or fewer points.
This does mean that a queen trade in the opening goes directly to endgame, for example Ruy Lopez Berlin. Castling and king safety is less of a priority; the king has become an attacking piece.
Inspiration was an idea: adjournment becomes available when the endgame begins, and players can carefully study the position, improving the quality of endgame play. Less radically, a new time control at the start of endgame.