The good news is that the latest version of Micael Scott's "Programming Languages Pragmatics" has a whole new chapter dedicated to scripting languages, and mentions Rexx various times. The bad news, however, is that coverage is sketchy, no doubt because it is impossible to know every programming language intimately, but to Rexx this is particularly unfair, because although its age is mentioned and it gets a honorary mention as forerunner of this whole field, lots of the good parts of Rexx are largely neglected.
Rexx is even not mentioned in the chapter that has a short description of every language that is mentioned in the book. Rexx's great assets, like unlimited precision arithmetic out of the box. the unique 'parse' and 'trace' statements, incredible string handling, object orientation including metaclasses, runtime addition of methods and properties, reflection and concurrency, are not mentioned at all. It might be that it is an old language and some languages have caught up with it more or less, but that does not mean that we need not mention the genesis of thing in the right historical order. The problem was, I think, that Rexx has been closed-source IBM proprietary for a long time of its existence; if it had been opened up earlier there would have been no reason for Python and Ruby. Larry Wall, who did Perl, visited one of the first Rexx Language symposia to explain what he thought that Perl had to offer, and indeed the similarity between Object Rexx and Ruby is enormous.
I think it is our duty to be at the same time thankfull to Scott for mentioning the root of scripting and mentioning Rexx in his book, but also to correct him in his fairly superficial treatment of our favourite language.