A way around this is to move the JIT to the kernel or to a different process. I would guess that that would hinder performance so much that, in typical usage, JIT-ting becomes too expensive to speed up things
Having the hosted browser in a different process shouldn't be too expensive. That's what Chrome and IE do. When you open up a UIWebView and process gets spun up that hosts the JIT (amongst the other plubming for the browser) and the host just has a window where the rendering takes place. This also fixes a whole host of other security problems hosting a browser in process.
Chrome and IE run on systems with faster processors and Gigabytes of RAM. RAM, especially is tight on iOS devices.
I also guess that some iOS apps will want to overlay stuff on their web views, postprocess the data, register callbacks, etc. Supporting such use might be a bit of work that Apple hasn't done yet.
Having the hosted browser in a different process shouldn't be too expensive. That's what Chrome and IE do. When you open up a UIWebView and process gets spun up that hosts the JIT (amongst the other plubming for the browser) and the host just has a window where the rendering takes place. This also fixes a whole host of other security problems hosting a browser in process.