Although it is difficult to think of anything that is not possible today, I imagine plausible would be a better term to utilize the onset of a tablet with a larger harddrive and a qwerty pull out keyboard.
Reading on a smartphone is very difficult for many, especially our elderly.
The tablet is strongly becoming the alternative to every portable device, especially among seniors. Will there be more companies introducing new models at a deeper discount? Probably. Will the demographics expand to include the older crowd, definitely.
Do we need to add more companies? Well, that's like asking that if we have a Facebook account, do we need a Twitter account as well. The answer I give to all of my clients is simple. Yes. No. Well, Maybe. Additional operating systems challenge the current OS. Additional chips challenge the current chips. Do we need a Kindle when we have an iPAD? The newer models will provide the combination of what the above have, but supply will meet demand and with the increased demographics, there will definitely be more demand.