Is the open source driver that comes with the ubuntu distros(specifically ubuntu mate 16.04) able to crunch anything gpu related? Any word on when amd will come out with amdgpu or whatever they are calling the replacment? Will this be a drop in replacement for fglrx for 16.04 when in comes out? I searched around but I can't find anything about how far away this driver is for 16.04. Should I just go ahead and drop down to 14.04 till the end of the year?

I suppose it depends on what GPU you have.

AgentB is successfully running RX 480 with amdgpu driver over at Einstein. It seems that driver doesn't support older cards yet. RX 480 Results

And other people are running Mesa OpenCL with older cards. Mesa OpenCL then doesn't support newer cards yet. See All Einstein@Home jobs fail immediately on starting and the linked threads.

Yes the new AMDGPU supports GCN 1.2 and later, and is much easier to setup than the fgrlx. The driver is a lot more stable than i expected.

See also

Ubuntu 16.04 LTS Is Deprecating AMD's fglrx (Catalyst) (released this month)