overgeeked
Open-World Sandbox
Fnord.
Not so much. Orcs and halflings were specifically excluded by the authors as being too much like Tolkien. Dragonborn are definitely a no no considering that absence of dragons is also a huge plot point, the use of draconians as the bad guys, etc.There are fundamentals of the setting and there are accidents of the setting. The fundamentals need to be kept, the accidents don't.
For example in Krynn (as you mention between the Cataclysm and the first novel) it is a huge plot and worldbuilding point that there are no true clerics. No clerics is right there in the elevator pitch.
Meanwhile, with the arguable exception of dragonborn it is an accident of the setting that there isn't a weird tribe of orcs somewhere in the mountains, or a couple of halflings somewhere or granddaddy sold their soul and so we have a tiefling.
Any races introduced after AD&D2E are more likely to fall into your accidents rather than fundamentals. But those come down to whether it fits with the setting or not. Something like a changeling might, or it might not. But a rabbit-folk? Not likely. A tiefling? Maybe, sure someone's ancestor sold their soul, but in a setting that's explicitly about good vs evil on a grand scale, maybe...maybe not. A villain? 100%. A PC? Probably not.
Yeah, people spend a lot of time trying to get out of constraints rather than accepting them. I'm not sure how creative it is to be told "no" then knee-jerk fight against that. It's a common reaction, yes, but it's not particularly creative.In my experience the main creativity fostered by constraints is the creativity in subverting the constraint. And the more constraints you put out there the more peoples' inspiration and attention is going to be grabbed by seeing how they can subvert those constraints.
If you want people inspired by your setting point to that which is inspiring and treat them like adults. If you bang on about how "we shall have no wizards and arcane magic is feared, and no clerics because the gods are dead" then you'll get the situation I saw at one Dark Sun table where there were no wizards ... instead there was a bard, a pact of the tome warlock, a druid, and a paladin. Because every player had their inspiration grabbed by the restrictions.
Also, maybe I'm weird but "treating people like adults" includes expecting them to follow the rules they agreed to and not whine about it. Setting up a game with constraints then having players rail against those constraints is functionally identical to a player complaining that they're out of spell slots and should get more. Sorry, you agreed to play this game and here are the rules you agreed to. You agreed to limited spell slots when you created your caster character just like you agreed to no orcs or clerics when you agreed to play this Dragonlance game set between the Cataclysm and the novels.