All is in the title.
software : compatibility ZERO/DUE --> common libraries ?
Doubtful. I fear that for the Zero, you will even have to use a different IDE, in order to use the onboard debugging chip and it's associated capabilities.
hardware : date of availability for all ?
The TRE was announced there over a year.
They offered 50 Tre's as developer version in May for the somewhat outrageous price of Eur139 IIRC (that were at that time US$200!), that doesn't look too good for the Zero, for which no price was mentioned when they apparently gave away 20 preview/beta samples in August to a select few...
Yes, announcing new stuff is one thing, actually providing them is another. But then those new boards (including the Yun) are apparently not directly developed by the Arduino folks themselves, but 3rd party devs, the Yun by some folks in Switzerland and the Tre by the BeagleBoards.org guys, which are providing the Linux part (based on the BeagleBone Black). And the Zero seems to be a bit of a marketing vehicle from Atmel for their EDBG (Embedded Debugger) chip in connection with the ARM Cortex M based MCU...