I can see an all in one tablet like device that would be good for Periodicals as well as all the PDA/UMPC functionality. But I think that a cheap greyscale book reader will always be popular due to the fact it is easy to read on it.
At the moment I have a specific MP3 Player (which can also do video, but I don't), a PMP for AVI (which also does MP3, Photos and eTexts, but I don't), a Sony 505 (which can also do MP3 and Photos, but I don't), a blackberry which is only used as for phonecalls/texts/emails (work), and a Sony UX380 which I use as my home PC. Each one does it's single job well.
I prefer to have a gadget for a specific purpose, because they are good at that purpose. I'm not interested in a jack of all trades as it is usually let down to functional compromises.