Hi Lawrence,
I've tried to publish access 2013 web app to office 365 preview edition.
The steps are as follow:
1. Sign in into the Access 2013 RTM with the account of office 365. (For example, yoyojiang@MSDNAccessForum.onmicrosoft.com. This is the account I got when signed up for office 365 preview.)
2. When create access web app, the site for office 365 shows up.
3. Then the url info of the app can be seen in the info tab.
4. The result.
Please do sign into the access 2013 with the account for office 365 when trying to create the access web app.
If there is an error which says "An error has occoured", please click OK>go to Office 365 preview Team Site >click Site Contents>find the app and click "Click to retry",
Thanks,
Keats Ge