OK. Here's my $0.02.
1) Xcode 6GM crashes every single time for me. I am running 10.9.4. I have no idea how widespread the issue is, but it is 100% repeatable for me. I cannot use Xcode 6 to submit apps for review.
The crash happens during the upload. I have submitted a RADAR report and given crash logs.
2) I was able to submit using the App Loader. Here's how you do that:
2.1) In the Organizer, after you have done the Archive, select the latest archive for submit.
2.2) Instead of "Submit," select "Export."
2.3) Select the first choice (App Store).
2.4) Open the Application Loader.
2.5) Select "Choose."
2.6) Select the .ipa that you just saved in the export.
2.7) That will work. You may get a message teling you that the API file is too big for analysis. I got that for all 9 of the apps I just submitted. In my case, I ignored it.
I think they rewrote the whole application load from scratch, and that Xcode is still buggy as hell.
They had a deadline, and rushed it. It shows.
I expect both the server (Web) component and Xcode to apply patches soon.
In my case, I'm quite annoyed, as I had to rush out a fix for the arbitrary decision they made to change the way that the CLLocationManager works, which broke all my location lookups. The fix is simple, but there will be a period of time when I receive hate mail from the users that upgrade to iOS 8, and the app stops working.
Joy.