Many Smartphone chips are already 'HSA' with a compliment of high speed 32 bit Application processors, multi-thread DSP, video acceleration, low speed 32 bit management processors, vector engines for the modems, acceleration blocks for cryptographic functions, HD video, audio, plus embedded power and clock management. If that isn't HSA, I am not sure what is.
I'm actually a bit surprised this hasn't happened before. AMD currently makes Intel X86 compatible CPUs. but there's no reason they shouldn't make CPUs with ARM cores. (Intel used to, in the Strongarm division they originally got from DEC sold to Marvell.) And AMD won't have any "not invented here" issues with doing so. AMD makes and sells chips, and ARM processors are poised to make a run at markets AMD is active in, so being able to offer X86 and ARM solutions is a compelling vision.
"Even if some of them DO share the vision, commercial competitiveness may persuade them NOT to join HSA on the grounds that differentiation is achieved by working separately or in a different group. Market pressures sometimes do that to technology."
This is part of the problem. The other which is inferred by the success of Intel in the PC business. In the short term it is very compelling not to compete with yourself.