Re: It was designed to fail
"I recall running Solaris 7 (I think) on x86 and it was OK (not fantastic or anything). But sometime after that the x86 offering went away and came back a year or so later with a slightly different name and some associated Sun x86 hardware"
I ran Solaris 8 x86 edition. Even had the official Sun media folder - was pretty happy with it performance on the cruddy little Pentium box I had at the time.
I concur with a previous commentard that it was Solaris 9 which dropped x86 support - I have definitely run Solaris 10 on x86 and also I think x64. There were some bizarre changes happening at Sun around that time - would be interested to know from the ex-Sun product dev above what the inside story was!
For an enlightening history of Illumos, there is a fantastic presentation from a guy at Joyent somewhere on the 'net, who originally came from Sun. Illumos is a great OS, and I hope has a long future.