I don't know if there are any dock related rumors, but letting others manufacture accessories would definitely cost Apple money. It would be cool, but Apple would probably lose more money than if they limited this to BT, even the use of a physical KB or game controls.
People pay to get certification. Apple's cut in accessories would be good.
How could it cost Apple money? Why?
Look at the page by Apple - they're putting Accessories on a par with
- In App Purchase
- Apple Push Notification service
- Peer to Peer Connectivity
- Maps
- iPod Library Access
Enhance your accessory by developing an iPhone app to extend its functionality, or create entirely new integrated solutions that combine an iPhone app with dedicated hardware. For example, you can display a fully interactive Multi-Touch equalizer for your speaker system. Create an inventory app for your barcode reader. Or, build an app that logs and tracks the readings from an attached heart-rate monitor. The potential solutions are limitless.
Create your own protocol.
Apple provides the information, companies pay up to join, NDA, then work on an accessory, and Apple can then approve or not. Your Bose music station already does this. Your MobiJuicer battery pack etc.