Our renderer is based on ES 1.1, so custom shaders are currently not possible. However, if you tell us what you want to achieve, we could integrate it to the engine. We also plan to switch to ES 2.0 mid-term, that is roughly til the end of 2012.
And yes, we have enhanced the UIKit plugin with a custom AppDelegate, and also added lots of iOS features including multitouch support, GameCenter integration, orientation support, retina support up to iPad3, local storage, custom fonts from the QML font loader, and low latency audio.
Considering you have existing logic in Obj-C, I guess you have your wrapper logic for the QDeclarativeItems in C++? With our plugin system, integration of custom C++ and Obj-C code is fairly easy. More news on that are coming the following weeks. The Xcode templates, together with the public plugin system should be available until september.
Regarding the pricing: building for the desktops, as well as Symbian & MeeGo is free. Using our build servers for iOS and Android is limited with the free version, but development and local testing on the device can be done with the free version. For deployment to the App Store and Google Play Store, the indie licence will be 500€ as an early bird discount. We did not finalize the prizing on custom builds, but for early users it will be the price of indie license!
If you have any further questions, I’m glad to help out.