Last I looked (a few years ago) ios forbid open source apps on the store, has that changed?
Which is one of the points of the GPL, so no big surprise.
One way to keep the option of legal offense against clones is with differently-licensed assets. MIT your code, but choose one of the non-commercial or share-alike Creative Commons licenses. There are lots of them and you're bound to find one that fits your purposes.
Apple has no problem with Open Source. It is just that a few Open Source Licenses have a problem with Apple. A small but important difference. Apple couldn't care less what open source license you use. But some licenses like the GPL forbid you from distributing your work in a place like the appstore.
Apple has the opinion that they should still retain control after a device in sold, giving them practical ownership after sale. This method of corrupting property laws for leverage over other peoples property goes directly against what the author of a GPL software wants, and is such written into license.
Apple with their appstore has thus a fundamental disagreement with the wishes of the author to GPLv3 licensed software. The author can give apple permission on this issue, allowing distribution on the appstore (if Apple accepted it), but that's a copyright concept. Authors can always give permission to someone else about their copyrighted work, but so long the author believes in property laws and peoples right to be in control of their bought devices, its unlikely they will give Apple that extra permission.
The GPL (v2 anyway, unsure about the others), forbid placing any restrictions on the rights to modify and use the software.
As running modified applications on iOS requires a Developer License from Apple for a fee (and associated additional Terms), some believe that the GPL is fundamentally incompatible with the Apple App Store.
Any license that imposes a similar condition (other GPL variations etc) are also likely to be incompatible with the App Store.
Disclaimer: IANAL.