Efficiency; download and update at the same time

There are a number of reasons why that will never happen.

1) Windows updates download based on server availability, rather than in any particular order, although the order can be tweaked a little by unchecking unwanted updates.
2) Windows Updates are downloaded installed using Component Based servicing - and some components may not be available for some reason at any given time.
3) each update has its own requirements for the existing installation before it can even attempt to install itself - and this is an almost unbreakable rule, by design.

Thus, while the order of download is pretty much semi-random, the order of install is a tree/branch process, such that certain updates MUST be installed first,, then others, etc..
Each update belongs to a particular branch on the tree, and this may affect later updates - even blocking ones that have already been downloaded.

Downloading and installing en-block also reduces the number of necessary reboots, as the installation order is optimised to allow as many installations as possible in the same session - installing in the order of download would cause may updates to demand a reboot which would otherwise be hidden within the mass-update session. We see this effect when we pick-and-choose updates from the available list for install, where some will happily install, and some fail, demanding a reboot prior, or another update be installed first.


In short - it ain't never gonna happen, both by design, and by necessity, and by long-term efficiency.

Possibly - but do you really want WU moithering you for a reboot every 5 minutes?

That what it does - but installing piecemeal in such a way as you suggest would mean that it would probably be asking for reboots after every patch.