Let me preface this with noting that there have been a *lot* if "feature request" threads. There are some posters who have come to really dislike them (though why such posters continue to read them is beyond me).
PiAhoy wrote:Disclaimer: These are only suggestions, so don't get your hopes high.
Boot from USB/USB 3.0, and use the SD card slot as a reader(or for a second OS)
Boot from USB (and bear in mind that on the Pi B series that includes the Ethernet adapter) is a work in progress for the Pi3B, and *only* the Pi3B.
While Gb/s Ethernet is a distinct possibility, SATA is rather unlikely (I commend to your attention USB to SATA adapters). However, getting either of those depends on...
Normal USB 3.0 (not for booting, for storage)
One shudders to think what an ABnormal USB 3 would be. USB 3 is very likely going to wait until Broadcom shifts from 40nm process node to 28nm. So USB 3.0 is pretty likely in a future generation of Pi. The boot from USB issue has nothing to do with what sort of USB is on the SoC. It has to do with the correct code in the boot ROM of the VC4 (which the 2837 SoC has) and a second stage bootloader that can support the process...and that is being worked on. With a bit of optimism, I would expect to see boot from USB in a general release of Raspbian within the next 1 to 3 months.
Upgradeable RAM of sorts
You mean "field upgradeable? Not going to happen. Closely examine a Pi board and think about *how* you would change out the RAM package.
Already present on the Compute Module (4GB). There is a CM3 in the works. No idea how much eMMC the CM3 will have. We'll find out in a few months.
Shutdown button on the board
Google is your friend. People have implemented such things. The real issue here is that Linux is inherently a multi-user/multi-processing system. Just pushing a button to shut down a Pi is not actually a good idea. A button to power it off once the system is shutdown would be okay, though. If this (and a SATA interface) is really what you want, take a look at the Western Digital SATA adapter board. It uses a CM, has a SATA connector, and also has a power button.
Certainly possible...but not likely in the near term. Does beg the question...where do you want to put it? As a USB port, or as the power connector? As a power connector may become necessary at the rate recommended current to fully power a Pi and peripherals continues to climb.
(mini) PCIE slot
PCIe is pretty specific to Intel x86 architecture. Sure, there could be some slick uses (e.g. M.2 connector), but space contraints, licensing costs, and shoehorning in an "alien" interface pretty much rule it out. What it really comes down to is, the Pi is *not* conventional desktop machine. It's also hard to see where a PCIe connection would fit with the educational goals for which the Pi was developed.
And stuff like faster WiFi @ 5GHz and AC WiFi, more RAM, heat-efficient processor, better heatsink/fan support, more RAM, DDR3 RAM, etc.
I will stick my neck out and hypothesize that you really don't understand the Pi very well. You are basically asking to turn it into a desktop "PC". That isn't what the Pi *is*. You can *add* 802.11ac to a Pi using an external WiFi adapter. More RAM...probably will happen--at least potentially--on a future Pi. Can't happen right now because the VC4 can't deal with more than 1GB. If you really need more RAM, there are 2GB boards out there. You just need to decide what features of the Pi you are willing to give up in the trade-off....starting with a reasonably current kernel and good software support. Later versions of DDR will also probably happen, but you're still not going to be swapping or adding RAM modules yourself.
Heatsinks...a major point of ARM designs is low power. The idea is to not need a heatsink, let alone a fan. Yes, I know that some people have thermal issues, particularly with the Pi3B. That is *probably* because, as a 40nm part, it is pushing the limits of passive, bare package cooling, especially when heavily loaded. Shifting to 28nm should make the SoC run cooler and is pretty likely to allow at least a modest clock speed increase.