"There was nothing magical about them" and "they had magical origins" are contradictory statements. Also, getting rid of the main thing that made many DMs and players hate the race (genetically-enforced kleptomania) is overall a beneficial thing to the setting and game overall.
They aren't any more magic than dwarves, who were also created by the Greygem's chaos, which also was responsible for thanoi, kobolds, bugbears, ALL beast-like creatures such as griffons, sea elves, shadow people, sirens, hobgoblins, trolls, and giants. Their origin isn't magic. It was Chaos. This all goes to the notion that if you strip away pieces of Dragonlance and its lore, it ceases to be Dragonlance.
How races came to be on Krynn, including every humanoid beyond the core of Ogre, Elf, and Human, is special. As an author, I'd be pissed if someone came in and said "that's neat, but let's do this instead and call it the same thing." It's not the same thing, not anymore. But, I should come to expect it. Hollywood butchers books all the time.
As to folks who hate kender in parties (and for those who are speaking from experience, not theory), was it because the gamer used the justification "I'm just playing my character" to be an ass to the rest of the party? I had a couple great gamers who enriched our sessions playing kender over the years.
I've seen the same excuse for "I'm just playing my alignment," and I consider playing a disruptive character to be a player issue, not a setting issue. Team players don't steal from their party, and that's not what Kender have ever been about.
1. Kender, as written, were absolutely loathed as a race. Probably the most banned race in the history of the game. Yes, I'm not saying it was universal and obviously some people liked them, but, as written, kender were a huge problem at the table.
Some support comes from the supplement
Mists of Krynn, which suggested kender should be an NPC race given the difficulty people had understanding playing them. As I noted, my gamers didn't aim to be asses to the group in the name of "roleplay." Again, I consider disruptive play at the table under the umbrella of "just playing my character" a copout for poor gamesmanship. But, I get the argument. It was enough of a deal for other tables that someone recommended shelving them in official product.
2. WotC wants to bring back the race because, unlike at the table, in the fiction kender are very popular and also one of the cornerstones of the setting.
You cite them as the most loathed race and banned from tables, but then a very popular one that WOTC considers so popular they need to come back. If they were so loathed, could there be argument to simply remove them from the game?
Greygem of Gargath cursing the lawful races to make kender - a not so nice analogy to Romani
Kender weren't cursed to be wandering gypsies that stole from people. Various AD&D and 3E supplements supplied quite a bit of complexity and lore to them in that they are eternally curious, have towns and (loose) laws, marriage rituals, and complexity that generally isn't seen by other races who stereotype them. Dragonlance's novels and the post-Cataclysm setting dealt with the ease of stereotyping and sticking with your own. The Companions were unique in that they defied that trend.
But if someone wanted to play kender that way, it could be done. See my above comments about disruptive gamers and stereotype gaming.
Feywild to Dragonlance - not a bad idea in a setting where elves play a HUGE role.
Elves aren't feywild in Dragonlance and have an origin story disconnected from any Feywild. This unique origin story gets trampled if it gets diluted into "every other generic D&D" setting. Fey didn't exist when Krynn was created, at least not until some animals were morphed into magical creatures, and some humans were morphed into Sirens. This goes back to a beef with 4E Dark Sun which did its damndest to fit everything but the kitchen sink into a Dark Sun reboot because it didn't want to split the market like TSR. They needed most everything in the PHB to fit and that's been WOTC's model.
But, in doing so, I circle back to "how far do you go until it isn't Dragonlance, or Dark Sun, anymore," but simply a world with dragons that you call Dragonlance?
Can anyone come up with a reason for not making Kender Fey that isn't based on nostalgia or appeals to lore? How would keeping things the same be better?
Yes, there's no rationale for them to be Feywild. It isn't needed because the setting has no connection to Fey. It's not an integral part of the world and never has been. The argument would be the same if I proposed that we make Dwarves into Fey because they too were created by the Greygem. There's no value or logic to it.
As to keeping things the same, mechanically I'm in the process of a 5E Dragonlance conversion, and kender are part of that project. I did the same for Dark Sun. I'm of the opinion the Kender Taunt should be an opposed skill check that reduces attack efficiency against anyone but that kender, that pockets should be eliminated as a mechanic and instead simply a roleplay feature to enrich, not agitate, storylines (finding a colored rock in the shape of a bull's head and wondering at how it got created), and that they shouldn't be able to pull crowbars out of pouches like some type of magician pulling rabbits out of hats.