The MRT steps should be the same for the new version. Some users have reported issues with multiple insert and MRT, so I'm actually looking into those now and making bug fixes if necessary.
Unfortunately I couldn't offer additional discounts for BETA participants. The discounts are already pretty steep and I'm trying to fund the update of Design Extender and power CMS to MySQLi. Hopefully that will be next after all of the kinks are ironed out in DataBridge.
You can already use the same database across multiple sites if you set up your database to allow remote connections. I'm not sure what you mean by variable support... If you expand on what you are referring to I can comment on it more.