IMO, the devs should be less afraid of this than the users, but many of those users who will do this really don't know as much about their phones and how they work as they think they do, so they won't know enough to be afraid of it. Right now apps are sandboxed. I use Password Padlock to store many of my passwords. But if I jailbreak my phone, how do I know that this information is still sandboxed? What's to keep a less than moral developer from writing an app that takes advantage of the unlocked nature of my phone? An app that looks like a fun game, for instance, but an app whose real mission is to root out all of the personal information in my phone.
Yes, there are good things that can come from hackers and jailbreaks, but sometimes those good things can be used to bring about bad things.
It all depends on how the "jailbreak" is delivered. For example, on WP7.X, you really had 3 options.
1. Dev unlock= side load apps, limited amount per MS, no system access
2. Interop unlock = system access but, not to the file system, allowed unsigned apps allowing for custom settings.
3. Root access = complete file system access as well as everything else.
If you played with your WP7.X device, you would know, Dev or interop unlocked required software changes (depending on the version of WP you were on) but, if you wanted root access, you HAD to install a custom rom. So a interop unlock is what MOST people here would be more than happy with, unlimited side loading and enough access to do registry changes (allowing for Teathering, custom tile colors and 3-row tiles plus more).
You have your apps in the store, IF someone pirates these apps (and it is possible to hack WP8 apps, due to the ATIV S that you can thank), they are coded. I don't think it is possible for someone to take a retail app, pull it apart and use it to pull your data. Even IF you could do a interop unlock, these "hacked apps that you speak of, could not even access the folders where you data is, so sandboxed apps would be fine. Now if your had root access, it could open this up but, on WP7 root tools(created by Heathcliff over at XDA), it came on most custom roms, that you can select the app you want to have root access, if you did not select an app, it would be just like it is now.
So, If you root your phone and STAY with just retail apps with a few tools, your phone STILL should be safe.
At this POINT, if this hack/jailbreak is real (at this point, it's just a rumor), only thing they showed is 3 row tiles, that needs Interop unlock and if they got that far, no question, your data would be safe...
I'm waiting on the sideline for this to happen if it will, AND I will wait for the experts over at XDA to take a look to see how safe it is....
It will be interesting if it's true...but, time will tell...
Edit: If anyone is wondering (This does not teach anyone how to pirate) how people are pirating apps with the marketplace encrypted ? So everyone knows, as I did some homework on this as I was wondering. People use a Rooted phone (ATIV S in this case), they download a demo of an app, when you download a demo, it's the full app but, locked with a key to the demo. So they download the demo to a phone, unlock the key, download it back to the computer and upload it somewhere. The limits to this is, If there is no demo, someone needs to buy it to rip it....funny how pirating works...You need to go to the very questionable sites if you want more info, that I will not provide..