You are overthinking things. Add anything you want to your Dragonlance campaign, it's trivially easy.
If you want to add a racial option not present in the canon, the "spelljamming/planescaping" option is just that, ONE option. I'd just add them into the fabric of the campaign. Want to play an orc, a goliath, a tiefling in my Dragonlance campaign? Sure, we'll find a way to make it work without the need to say, "You are a visitor from another world . . . ."
Same with class options that didn't exist when Dragonlance was first created. It's very easy to find a way. If you are playing a Dragonlance campaign BETWEEN the Cataclysm and the War of the Lance, then you are doing something very focused (no divine magic) that requires conversation and buy-in with your players. But really, the upcoming book and most folks DL campaigns take place DURING the War of the Lance, when clerics return to Krynn. If a player wants to play a cleric, who cares if Goldmoon hasn't found the Blue Crystal Staff yet? Your PC's god just "activated" them around the same time, maybe even a little before.
If you want to have a character who is a visitor from another world . . . that's the least creative and interesting option, IMO, but okay. If they are a cleric of a non-Krynnish god, you have all sorts of options. Again, are you playing BEFORE the War of the Lance and the return of clerics? If not, it's not really a problem. If so, any cleric is a problem, off-world or no. Why do you have to go through mental gymnastic to explain why the follower of Paladine can't cast spells, but the follower of Lathander can? Just rule, "no divine magic" in your campaign. You don't need to give player's a reason, as it would be a mystery to the characters. But maybe the High God restricts divine connections from deities not in the Krynnish pantheon.
So, so easy . . . .