Have you heard of GT kids getting turned away? I have extended family up by you. They enrolled from out-of-district to go to the IB program and didn't have any problems.
No, but I don't personally know too many people who have choiced in from out of district. Those I do know don't have gifted kids or at least don't have kids with a GT id.
Our assigned school in district does actually have an IB program and the middle school dd is currently attending has an IB MYP. The school she wants to choice to isn't overly full and does not have IB, but dd feels that AP may be a better fit for her and I'd tend to agree.
The main issue for her is demographics. Her current middle school has about 16% of the kids ided as gifted. The demographics of the area it draws from makes it likely that it would have fewer than an avg amount of gifted kids whereas the school she wants to attend draws from an area where it is likely that there will be more kids like her. She wants a more challenging high school with more intellectual peers rather than a school with a lot of kids with GT ids where they have to teach to a group who doesn't learn like she does in the accelerated classes.
She finds that the classes that are full of high achieving non-gifted kids don't approach things the same way. The ones she has enjoyed the most have been things like a quarter long writing pull out where the GT coordinator only took maybe 20% of the GT ided kids in her grade or a workshop that only had 5% of the GT ided kids so they had kids who were likely actually gifted or at least close.