I might ruffle a few feathers in the Purist's camp. (Yes, you Luddites are in for it!
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I'm going to take the stance that more is not a bad thing as long as people are not forced to experience it. For a biographical piece, and any number of other specialties, it would be pretty cool to have hypertext links to documents, web pages, etc. that might enhance the experience. I say, let them create the Mbook(Multimedia) category and let's benefit from it when we can. I'd still want a plain text version of most ebooks, but if they want to create another category who is anyone to stand in the way of progress?
I wonder how many would really stay purists if the enhanced multimedia content was handy and the typical ereader capable of exploiting it... Go on, you know you want to. You do it. Everybody does it. I do it! I did it twice this morning, and I'm gonna do it again. You know you want to. (with respect to Mel Brooks, It's good to be the King!)
This issue may soon come to a head if e-ink displays go color with better quality. There is no reason why Mbooks couldn't be written and displayed on Android or iOS devices except for the lack of a relevant standard and a "reader" app capable of the format.
I'm not saying that books, or ebooks must go that way, but Mbooks just open another revenue stream and may pay off big time. If we play our cards right we may eventually make it to the fully interactive experiences that could really be interesting. Imagine reading(experiencing) stories from the author's standpoint, then from another person's or many other persons if sufficient pathways and choices were offered almost like a ZORK interactive adventure, but "played" by someone else and read by you as their version of story -could be interesting, the fan fiction crowd would probably bust a collective... Nut, anyone?