According to lore, Gruumsh once had an alliance with the conniving elven goddess Araushnee to bring down her fellow elven deities once and for all. Their plan failed and Araushnee was transformed into Lolth and her elven followers into drow.
If the elf PC, at WarpedAcorn's table, has the drow sub-race, then your angle has even more interesting opportunities for where the story might go.
I disagree with you about chaotic alignment and random arbitrary shifts of direction. Robin Hood is classic Chaotic Good; that doesn't mean he'll ever change his mind about taking from rich and giving to poor. If Corellan and Moradin ever relent and allow the orcs a homeland, even a desert or swamp, at that point Gruumsh's commitment to destroy "all that the other races would deny them" stops applying, and THEN he's free to change course.