Fair enough. But, OTOH, if they asked the same question about, say, orcs - "Should we keep orcs the way they are or redesign them as fey?" I'm thinking you'd get a pretty strong vote for keeping them the same.
Well sure. There is no existing contriversy over orcs as fey creatures and no argument advanced for that, so peoples immediate reaction is going to be 'Blegh'. So all you've created there is a straw man. You could however restate the question in a more analogous way, something like: "Do you think that orcs should be a playable PC race balanced with other PC races, or should they be inherently inferior and unattractive as a PC race?" Now, you have something to argue about, especially when you start extending the frame of the question to cover all sentient humanoids: "Do you think that bugbears should be a playable PC race balanced with other PC rares, or should they be inherently superior and dangerous as a PC foil?"
But even your straw man can be reframed into a powerful contiversy with just some slight rewording a building a bit of an argument. Suppose I made the following argument:
a) Goblins and orcs are generally too similar and occupy the same design space of evil ugly humanoids. Goblins originally existed mainly to be a weaker orc for lower level parties to fight, but we don't really need that separation any more.
b) The term goblin historically refers to an evil fairy creature.
c) What if we kept the concept of 'orc' as a Tolkien inspired evil, ugly, humanoid but made goblins evil fey creatures to make them more distinctive?
I'm not sure that there wouldn't be strong advocates on both sides. For my own part, Trolls long ago made a move from being grotesque regenerating giants, to large ugly fairy creatures precisely because the historical usage of the word 'troll' fits more closely with this later idea and equally because it makes trolls far more interesting as NPCs especially in a game like mine where I feel Grimm's fairy tales are a significant influence. It's hard to imagine a D&D troll playing a violin, or engaging in a game of riddles with the party. But if you make trolls fey...
The fact that Slaad don't get a strong vote for staying the same I think speaks pretty loudly that the monster as it stands, just isn't getting enough traction in the larger audience.
Yes, but I'd suggest that part of the reason for this is that they just aren't presented very often compared to orcs or fiends - either as foils, friends, or allies. Rightly or wrongly they are a fairly obscure monster outside of Planescape. It's not necessarily clear that if you designed or replaced them with anything that they'd immediately get traction and become an equally popular monster to orcs, giants, dragons, or demons. It could be that regardless of form they are pretty niche, and I think it is fairly obvious to me that a lot of the answers are simply people picking what they think is the best of the options presented. For example, I'm strongly on the side of, "Slaad are great, they just need someone to build on their lore." and "The worst thing that could happen would be to make Slaad merely another horrorific monstrousity.", but I also would have voted for 'Aberration' simply because that's the best of the available terms. Likewise, I'm also a proponent of Modrons, but would have also voted for 'Construct' as the best of the available terms. Neither vote indicates that I think they monsters need a complete rewrite, just a bit of elaboration and depth.