If Apple goes through with their new policy, then it is likely that Amazon and B&N and Kobo will pull their apps for Apple products. Which means the IPad will not do what you want it to do. If you are willing to wait you could see how this plays out and buy an IPad if the Apps remain available. If you need to buy something immediatly then I would hedge my bets and buy a different device.
The other thing to keep in mind is that the DRM on IBooks has not been cracked, the only one of the major sellers to remain intact. This means that books you buy through IBooks will not be easily moved to other devices if you should chose to go that route. The others you have the option, if you feel that it is legal and morally cool, to strip the DRM and sideload onto another device, like an IPad or a different e-reader.