Arc-descent conjecture for rational motivic cohomology presheaves

For an algebraic space $X$, let $\Cmot(X; \Q(r)):=\Gamma(X;\Q(r))$ denote the rational motivic cohomology spectrum with Tate twist $r$. For every integer $r\in\Z$, consider the presheaf $X\mapsto \Cmot(X;\Q(r))$. Arc-descent conjecture. For every integer $r\in\Z$, the presheaf $\Cmot(-;\Q(r))$ satisfies arc-descent. This predicts a stronger form of descent than the established $h$-descent for rational motives; the preceding discussion presents it as more credible than arc-descent for the full presheaf $\DM_\Q^*$, but the conjecture's resolution is not specified here.