I finally bit the bullet and bought a RPi 3, my son has been after me for awhile to do so. I think he figured if I got one I'd immediately fiddle around with it and make it do crazy stuff. So I did.
Primarily I wanted it as a portable media center, to be used both at home and in the camper. Didn't like the idea of needing to use an SD card, as the corruption possibility is pretty high on those. Saw how some use the SD to start the process, then use a USB drive (thumb or ssd) for the system. Finally found a way that allowed you to boot directly from a USB without the SD. That looked very promising. The directions I found to accomplish the task, while clear were quite frankly way too involved and I knew there was a better way. In addition, I wanted the system to multi-boot.
I realized that by setting the flag variable that would shift the register to tell the Pi3 (only works on this model) to allow a USB boot. So I first used Berry Boot to do an initial setup strictly to an SD card. Changed the flag variable and fired up the system. So far so good. Then used dd (I use linux as a primary system) on my main computer to clone the 64GB micro SD to a 128 GB thumbdrive to test the concept. Shut everything down, removed the SD, installed the thumbdrive and fired up the Pi. Works great! Presently I have OpenElec, LibreElec, Gnome Mate 16.04 and Raspbian loaded. I tried deleting operating systems and installing others using the standard Berry Boot system and it works great. Only thing is that with Raspbian I have to remap the dev from the SD card to the USB if I do a reinstall. But that can be done with a simple script and only needs to be done once. In addition, Gnome works well, but doesn't shut down fully. The two media centers work fantastic, using auto-switching VPNs for specific programs.
I read that supposedly if you set the flag, then you can no longer boot from the SD slot. In my case that isn't true. Tried it with only the SD, the SD slaved to a USB and then the USB solo. All three modes work.
So now waiting on my new SSD to clone the thumbdrive to. This is so sweet! A fully operational computer that uses 2.5 amp at 5 volts, is a bit bigger than an Altoids tin, has built in wifi and bluetooth. Not shabby for $35.
If anyone is interested in the exact steps I did, I'll post them. If you want a clone of my system you need to send me either a 64 GB+ thumbdrive or SSD. On the clone, I'll have the VPN set up, but will delete my login info, sorry.
dave