I don't know if I'd agree that SPARC would've ever been viable. The performance just wasn't there for the price. For instance, my 2002 AlphaServer DS25 with two

I don't know if I'd agree that SPARC would've ever been viable. The performance just wasn't there for the price. For instance, my 2002 AlphaServer DS25 with two 1 GHz CPUs runs many workloads noticeably faster than my 2007 Sun Fire V245 with two 1.5 GHz UltraSPARC IIIi CPUs. Also, Macs were never locked down. All Macs can run alternate OSes, from m68k Macs which can still run modern NetBSD without issues, to beige PCI Power Macs, to G3, G4 and G5 Power Macs, to Intel Macs, and now ARM Macs. Notably missing is support for NuBus Power Macs which requires more work than people are willing to do, although older MkLinux was available for them.