You probably won't be forced to choose between a tablet or ereader or make other similar difficult decisions very much longer. One reason, of course, is that their capabilities are being merged in ways that may make a single device suitable for many uses - but that is not the main reason you'll avoid these agonizing choices. With all the uses for this versatile crop of new devices, it's very likely you'll have more than one. We certainly have numerous magazines and books on hand not to mention newspapers. If tablets, ereaders and smartphones become universal tools, a family will most likely have several.
After all, it's not uncommon to have multiple PCs in the house; it often makes sense to keep an older machine when upgrading since they have little resale value and work quite well at common tasks. Of course students regularly use computers for homework and the competition for "the computer" can get fierce in the evening.
It's important to note that we are in the early stages of the Mobile Revolution and dozens of different shapes and sizes of devices will come out soon. Distinguishing between tablets and smartphones will become increasingly difficult and naming conventions will evolve rapidly.
In any case, it is quite likely that a variety of tablets and other mobile devices will be used to replace collections of books, magazines and other publications. No matter how much we enjoy the feel of a "real book", we will rely increasingly on electronic means for much of our information and that means more electronic devices will be needed for access.