If Blizzard could go back to before they released WC3 and rewrite it to remove the redemption of the orcs, would they? I don't think so, but they'd think about it. It would be a hard decision. Why?
Intelligent, rational, kind, almost human orcs are not good for starting wars. Thrall doesn't want war with the Alliance. Jaina doesn't want war with the Horde. Other leaders don't want war either; they see that it is devastating. More importantly, now that the orcs are more than violent savages, peace is possible.
Imagine if there was no Thrall. Imagine instead that Garrosh had been leading the Horde, that he had been the one to liberate the camps and lead them to Kalimdor. It would be a much different Horde. It would be one in which we'd see much less problem with war. The Alliance would be justified in attempting to wipe out the Horde and in the same way the Horde would be justified in fighting for its survival. As it is now, the Alliance cannot justify war with the Horde, especially with immediate problems such as the Scourge and Old Gods.
As I think about it more, there's a lot of potential in an evil Horde. Much lore would need to change, but I think it could be for the better. Blood Elves would find themselves picking a side in a three-way war: Horde/Legion, Alliance, Scourge (who are now free of the Legion). They could still join the Horde, in order to fight the Scourge together, the Horde doing it to regain control of the Scourge. With this new lore, Kael'thas would not need to betray his people to side with the Legion, it would instead be the normal progression of increasing evil.
There are some bits of lore that would need touching up.
Fighting with the Old Horde in Azeroth would have to be more of a factional conflict with the New Horde trying to reunite those who had fallen under the sway of the Black Dragonflight.
Killing Kael'thas would be part of an internal conflict, a power grab by the leaders of the New Horde attempting to fully subjugate the Blood Elves and install a puppet in his place. Or it could actually go the other way around; a noble Kael'thas would see the terrible things he'd done and turn against the Horde and Legion in order to save his people from corruption. The Alliance can kill him because they don't know he's turned.
Fighting the Old Horde in Outland might be tricky, since it would still be allied with the Legion. I suppose something could be figured out: internal power struggle, regarding the Outland orcs as cowards for having been left out of the recent wars, maybe even replace Kargath with 'Thrall' and have the fight be one of the savage vs. the redeemed.
What would you change to make it easier for us to kill each other?