Depending on when you get your iPhone 5, you may or may not be able to set up active sync at all. But if you are happy with fetch, then you can set it up as a regular IMAP account anyway.
The only thing you won't be able to do is have push mail through the default iOS Mail app. You can do fetch through the regular Mail app, you can do push through the Google Gmail app. You can have both set up simultaneously, using the Gmail app to notify you of new messages, then open the Mail app to read them. In that case, you can leave the Mail app to manually fetch messages only when you open the app.
OK, I won't mind not using exchange, but what about google calendar syncing?