Why not just have François Ier outbid Charles V? Viola, Valois Emperor. Sure, Charles V has a lot on his side over the French King, but at that point there was not significant gold coming out of the Americas as many believed. American gold didn't win Charles his crown, it was Castilian Rents. He morgaged them successfully to the Fuggers for the funds needed. It probably helped that Charles V also neutered the pro-French party by driving the Duke of Wüttermburg into exile. Charles V was also not without his competition: The Pope was urging the Elector of Wittenburg to run and Henry VIII briefly tipped in his hat for prestige reasons.
Give Francis some better luck, thrawting Charles V's attempts in Wüttermburg and possibly having him sway the Fuggers instead by offering economic encentives, like perhaps a percentage of the Taille or Gabelle (both very lucarative taxes at the time), and he might beat Charles V. If say the Elector of Saxony does decide to play and Henry sticks it out for longer, perhaps the King of France can slim out a victory.
Having the Burgundian Valois is interesting, but Charles and his ancestors always seemed more interested in gaining a crown of their own, not the Imperial mantle. Charles the Bold nearly gained the crown of Burgundy but the Emperor tired of his arrogance and left Worms IIRC under the cover of night. I don't see why this male son wouldn't continue to pursue that claim.
Also agree with Jan; claims that Philip IV would be more "Flemish" is bogus. The Burgundian court was in the Lowlands, yes, but it was heavily francophone. Indeed, Charles V was too, and that was a big reason for the Revolt of the Comunneros because he brought all his foreign advisors to Spain. There were Flemings in his administration, yes, but the culture of the Burgundian court was first and foremost French. Flemish was still regarded as a vulgar tongue at the point. So be it François I or Philip IV* as Emperor, they'd be French speaking and at the head of a French speaking court. Very little seperated the Valois of the main branch of the Burgundian branch despite their dislike towards each other. They both spoke French and the Burgundian court model was widely copied abroad.
And also agreed; the language they speak means diggly squat. Even if they became Flemish, who would it disbar them from France? France followed Salic Law, not "you have to speak French" law. The surviving Burgundians are still superior to the Bourbons. Besides, Henri IV succeeded with no issues and even he was somewhat foreign, being King of Navarre and having been raised in the south of France. He was a real Gascon; he spoke with a lingering accent for the whole of his life.