OK, I have just thought another potential features for this kind of device: faxing digital documents, which is a useful feature to distribute/transfer legal documents (which potiential markets include businesses, governments, lawyers etc).
First of all, if sony or other makers want to make this feature, please do your own market research on faxing, since I am not really sure how big or solid this market can be, however I will leave links that I read about value of faxing in today:
why faxing is still relevant in the 21st centry
Why Faxing is Still Relevant
First, let me briefly explain about the feature in abstract level: That is to allow user to fax a pdf document (can be annotated as well) through a faxing option in the menu and/or via a built-in faxing application.
Second, I will speak on some of the possbility which I think this might be achieved:
option 1: Fax via a third party and WIFI. Partner with a internet faxing service provider. They are originally websites, which allows you to request a fax online, and they will fax it for you. Sony/other makers who want to make this feature can find them, and help them make a built in app on this slate, and/or built-in menu option on this device, so customers can use those services on this slate very easily. This is probaly relatively easy to do, since wifi is all you will need for connection.
option 2: Fax without a third party and without cellular intergration. Basically it is to have this device to fax through cell phone. The slate will connect to a cell phone wirelessly and cooperate with that cell phone to do the faxing. I am not sure if simply make an app on the phone can achieve this.
option 3: Direct celluar connectivity build in. Basically fax through this device directly. If a celluar integration is made, then there should be tones of other related feature (directly or indirectly related to the celluar connectivity) to be integrated to fully take advantage of celluar connectivity, like to use this slate to make phone call (with mic headphone, which means this slate will have a head phone jack as well.) And from that, we assume since if it has a head phone, then maybe we can also use it to play music? For battery issues, I assume user will only use the celluar activity when he really need it, and for the rest of the time the celluar should be able to turn off in order to preserve battery life advantage, so it is probaly not expected to wait for phone calls, unless sony decides to dramatically increase its battery power.
option 4: No third party but wired connectivity. let it connect to a phone line (maybe through a mini-usb to phone line converting interface), and use it as a physical faxing machine to fax.
Thats basically my thoughts so far.