What imperial backing? AIUI most of Marie-Maximilian's marriage, the empire was too busy dealing with Matyas Corvinus. Burgundy provided the funds and the troops to fight off the French. And what Louis XI's reaction would be remains to be seen. He's got the duchy of Burgundy proper, but the rest of the lands allowed female succession, which meant Marie.
Does Louis XI want Marie to marry Charles VIII? Yes. But Louis XI was a master politician. While he'd rebel against Burgundy being CONNECTED to/in PU with the HRE/England, the marriage of Dickon to Marie is a different matter. No personal union between Burgundy-England means that England has no access to Burgundian funding, OTOH Marie gets a sword to fight for her as OTL. AIUI Dickon's battlefield rep was pretty good. But Dickon-Margaret's "estrangement" from Edward means that Louis can exploit that to drive a wedge between England and Burgundy (same way he drove wedges between other allies OTL)
@isabella