ehh.... I'm not sure you could call ereaders a "doomed technology." Niche market, maybe but certainly not
doomed. The only way a multipurpose device would doom ereaders is if one could switch between an eInk and LCD mode on the fly.
*sigh*
Sooner would the market for physical books shrink to the point that Borders had to declare bankruptcy. Oh, wait....
I predict that eInk technology isn't going to be doomed by tablets, but that the technology will develop in time such that ereaders will some day have HD resolutions as well as color eInk, while still retaining the ability to read in direct sunlight and last for days and weeks on a single charge.
Niche markets do not a doomed technology make. Look at adventure games: someone might have once said that the market for adventure games was doomed, but if that were true Telltale Games wouldn't be making buckets of money on their games.