This is interesting when thinking about IBM, which outside of licensing the ISA to some designers hasn't always transfered its core IP to outside parters--with the rather unimpressive cores in the current-gen consoles versus their contemporary IBM cores as an example.
Perhaps it was a business model consideration, and IBM felt that IP was too valuable an asset to transfer. I suppose the question now is what changed, the returns from sharing, or the value of the IP and IBM's microelectronics division.
IBM might also be buying into the heterogenous HPC wave, or hedging its bets for cloud server tech.
Nvidia could use a partner that isn't in the business of providing GPU silicon or throughput chips. That leaves PowerPC as far as notable architectures go in this space, I think. MIPS is acquired, x86 is arrayed heavily against Nvidia now, ARM makes its own graphics IP and is getting muscled into by multiple GPU providers.
What slice of the original space does this leave for Nvidia's custom ARM core, however?
The inclusion of an interconnect partner shows how important that part is. Intel's bought interconnect tech and is about as aggressive on that scale as it is with the silicon it wants to push. AMD bought into something along those lines, for the dense microserver environment at least.