Why?
Because people have been BEGGING for Bethesda to not just let them keep journals... but WRITE BOOKS since at -least- Morrowind.
It's a good idea. It really is. And that's really all the reason you'd need to do it. How hard is it to create an in-game TEXT BOX what lets the player use their Keyboard (or a Playstation Keyboard, or the Chatpad Keyboard for XBOX 360 users) to input text? Honestly?
Do I think they'll do it... doubtful. Bethesda has a knack for missing ideas that have been being requested forever.
Do I wish they'd consider it? Oh, you bet.
I'm sure they've heard or had the idea thrown around. It's always a balance of features against resources, time, and direction. Not everything can be done. Plus again people like me would rather those resources be used elsewhere.
I highly know the immersion factor that would bring and I'd imbrace it in Fallout, which I hope they go all out in the work and resources department. I personally couldn't care less if The Elder Scrolls drowned in the Great Salt Lake never to rise again. I highly think it profits off innovations made by Wasteland and Fallout in the first place. I digress.
I discount it here because they do have limited resources and again think it's better served elsewhere. I mean I'm sure there's a thousand better uses you an think of.
And realistically they as you say haven't added it nor have the time to in these final months.
Yes I realize I'm circling about. The subject is one of those if it's not there by now forget about it until the next project comes ones.