"installp" is a bit of a black art. For a long time, it was impossible to get build software without spending unnecessary amounts of money, so very few people outside of IBM (and Bull) were worried about this.
"rpm", on the other hand, has been freely available for many years. There should be no particular considerations for AIX for script-type material, so the vast amount of experience, knowledge, and code examples available for Linux will be useful to you.
I don't think IBM will let AIX go soon, but they are actively porting standard Linux tools on AIX and some of the AIX tools on Linux to make the environments converge. I think this is only a matter of time before installp begins to "depreciate" in favor of rpm.
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