Assuming the following is true (which seems highly likely)
...
Fortunately for us, Broadcom were willing to step up with a new SoC,
BCM2836. This retains all the features of BCM2835, but replaces the
single 700MHz ARM11 with a 900MHz quad-core ARM Cortex-A7 complex:
everything else remains the same, so there is no painful transition or
reduction in stability.
...
It should be compatible with all the existing Pi software but will also be usable with WIndows 10 and more modern Linux distributions such as the latest Ubuntu. For strike out text reason see second edit.
Until it gets on the streets we're all in the dark.
EDITED TO ADD
Unfortunately it looks like all the register addresses have changed.
The peripherals base address for previous (ARMv6) models was 0x20000000. The new (ARMv7) model seems to have a peripherals base address of 0x3F000000.
This will break all the existing low level C libraries (wiringPi, bcm2835, pigpio), bare-metal programs, and any code which directly accesses the peripherals.
If this is the extent of the changes it is fairly trivial to fix.
However it's hard to reconcile this change with the statement that no changes are required.
EDITED TO ADD
I was wrong to suggest that Windows 10 or Ubuntu will work on the Pi 2. There will be no support for the desktop versions. What is being touted is Internet of Things versions which are CLI (Command Line Interface) based and are aimed a servers.