I haven't actually built one of these, but my guess is that few bookshelves designed to be stationary will stand up to the stresses of being used this way. They would, at the very least, require significant modification.

Each section of a shelving unit that size might hold 300-400 pounds of books. Add in the weight of the shelves themselves and you need some serious hardware to carry them. No, furniture glides on carpet won't work. Large casters might work, but even they wouldn't roll easily over thick carpeting.

My biggest concern would be your comment about the priceyness of murphy bed hardware. No matter how you slice it, this is a sizable job and will not be cheap.

I unerstand this can't be done with Ikea type bookcases--but we have some unfinished furniture stores in this area where the product is locally made--not shipped from China and they might have product that could be adapted...

since the track system would not be used that often--certainly not even once a month on avg probably--barn door track systems that you see in some newer construction/design would certainly be strong enough to hold something like that I would think (not the kind that sliding closet doors use)

the bookcases would be more stationery than rolling...but I take your point about need for proper construction due to weight of books themselves if nothing else...

the point is that I would not order something like this that costs 3K for a wall/bed system on-line when --even if you spend that much to have it built on-site-- you can get a true "custom" construction and better control over materials

they build these by their standard dimensions--we can't really see how well constructed they are or the actual quality of the wood/materials used...
I would not spend that kind of money to order something w/o seeing at least a sample of the work--and there are none of the companies I found last night that have any product showroom in our area--DFW--

we have friend who is builder and he has some awesome trim carpenters...they could probably build this for us if they had a good blueprint with materials--but their deal is anything unfamiliar gets the price increased just because it is new--not necessarily any more difficult--just different--have a set of plans and material list would make it that much easier to get rational price from them...

we just saw it last night--have to measure wall it would go on and determine some factors like closet door swing and window on that wall to see if it could be done with balance...
although the house it would go in has two other bedrooms beside this one available for guests (we are empty nesters) there are some people who would prefer to sleep downstairs--and it would just make that room more flexible for me to use as my study/computer room...

the master in this house is smaller than I would have really liked (owners made other design choices to limit its size) but there are other factors that we like--just looking for way to maximize potential...