I think this leaves AIX the same place as before
It's one more option on IBM's systems. You can have AIX, Linux, Solaris, BSD, Windows, eComStation, Unixware, Netware, or whatever on IBM's small server x86 kit. They sell and support AIX, Linux, Windows, and now Solaris. It's business as usual for IBM.
The Solaris on z and on Power are intriguing, though. There are considerably fewer after-market OSen one can just throw on a Power, and fewer still on the big iron. If they get Solaris running smoothly both of those places, that'd be neat.
Also, don't think of this as necessarily one way. IBM has been trimming the fat lately, not buying more lines. I wonder what some collaboration between these two could do with AIX on Sparc. If Solaris can go to Power and z, there's no reason a similar team couldn't put AIX across Sun's whole line. Sun already does both Solaris and Linux. So this could, in the end, give both companies more options to sell to customers.
One strength of IBM has always been that their services people will work with you on anyone's hardware, too. Imagine a data center with mainframes, T2, Power, Rock, Opteron, and/or Xeon machines each doing what they do best (yes, there are performance differences enough on differing tasks to want both Opteron and Xeon if you're watching cycles closely enough, although who has what lead changes from one generation to the next of the respective lines), and all running either AIX _or_ Solaris. All of that could be backed by a service contract from Big Blue. The mind boggles.