What does this have to do with making media ready-to-hand?
I mean aside from the obvious: if we're not concerned with how/whether the media we're using works, we can shift our concern to what we want to get done with it instead. The idea of a seamless media experience is appealing on the grounds of being unobtrusive in our pursuit of performing tasks with media as our equipment. Take the example of the lumberjack who wants to cut down a tree, very reasonably so: if their axe is in working condition then they can concern themselves with tree-cutting, rather than the axe. If the axe is not in working condition, or if it's missing when they need it for cutting trees with, then their concern shifts to the axe. And that's not convenient.
Here is the issue: we're not using axes. We're using electronic media. We aren't using "crude" technology; we're using technology so sophisticated that we don't know (most of us) how it works, how to fix it if it breaks, or how to make it. Therefore, we rely on other people making it for us. (We probably rely on other people to make axes for us as well, but bear with me here.)
And who's making it? Microsoft are making it. Apple are making it. Google are making it. Billion-dollar multinational conglomerates are not only in charge of producing this equipment; they also own it.
Which is the issue with using Heidegger to inform a design philosophy for ubiquitous media: Desein is all about being concerned with ourselves and the world, but the impetus behind ubiquity seems to create an experience of non-concern, like the people here:
Just some paranoia for us to chew on while working on that book review.
(Basically I'm saying that it's incredibly suspicious that while the designers of ubiquity like Heidegger for his whole Desein thing they also seem to be trying to engineer a world in which nobody is actually Desein. Just to clear that up.)