Me, just because I can toss in a cheap Trinity on clearance until Steamroller CPUs finally (FINALLY) come out, then switch 'em. Native USB 3.0 support doesn't hurt my feelings either.
The native USB 3.0 support is the exact same support you get in existing Trinity motherboards because the FM2+ boards use the same southbridge. If you are buying this type of platform right now (and by "right now" I mean, you absolutely need to buy something *now*), then go with FM2+ just because of the upgrade option. If you really want Kaveri and aren't all that interested in having a chip floating around after the upgrade, then wait for Kaveri since these boards offer basically zero benefits to existing Trinity parts.
"existing Trinity motherboards because the FM2+ boards use the same southbridge."
Are you sure? I seen A88X, which would indicate that it could be a new chipset. However I have seen no info on the A88X, have you?
Fudzilla (yes yes I know) claims they are almost identical. AMD claims the chipset is brand new. Asus's website seems to back Fudzilla, however, when you look at the specs: http://www.asus.com/Motherboards/A88XMA/#specifications
That's the high-end version of the chipset and you are basically getting:
1. 6 SATA 3.0 ports (just like in existing Trinity boards)
2. 4 USB 3.0 ports (just like in existing Trinity boards)
3. Various assorted USB 2.0 ports.. nothing looking particularly different than what we've seen in the past.
3. The Asus website does mention some "UASP" support on USB 3.0.. not sure if that's really new, and if it is, not sure if that is part of the native chipset or some third-party addon from Asus.
4. The board does support PCIe 3.0, which is new for AMD, but the PCIe 3.0 is built into Kaveri and isn't part of the chipset (Trinity parts would still be stuck with PCIe 2.0).