True, weight and battery life are major concerns. I like the idea of the e-readers and let's face it, although a more or less one trick pony they fill a very niche market. BUT serve that purpose well. This is why I'm so on the fence.
I have a house full of books (just really started reading again after layoff) and have started to run out of places to put them. Here is where these fine little devices come in.
As far as the backlight. yes that would be a drain on battery, although having to carry around a light for dim reading is a pain as well.. not disturbing your partner in bed and others
To large for normal usage: I have had this argument before with my fellow techs. Their argument "hey you always have your laptop/iphone with you"
I argue, there are to many times when the iphone (for long reading) is to small and laptop impractical. The "tablet/KindleDX" type of device would and do also serve a specific niche. Newspapers/magazines, text books, ebooks (lets's say my current haul microsoft cert books) where a large screen is very nice.
After all, NOTHING is the perfect solution for everyones needs.
as far as "You can buy tablets today even ones that run macOS." I personally do not know of any other than the iPhone. we are not talking about hackintosh machines.