Please take the following with a grain of salt. I am not a legal expert, but we have competent US lawyers assessing this for us right now.
The main issue we see with the GPL is that your app has to be effectively licensed under the GPL too, which makes your app's license incompatible with the iOS App Store's terms of service.
This is apparently not the case with the LGPL. Yes, you will have to provide a way for users to relink your application to another version of Boden. As far as I can see (I am not a lawyer), this can happen outside of the iOS App Store.
Our US lawyers are currently investigating this. As soon as we get a reliable assessment from the legal experts, we'll add an LGPL option to Boden.