[Raion]

Nothing is more jarring for new users on IRIX than trying:

tar xzvf randomprog.tar.gz

And finding out that no; tar doesn't support compression

Clearly, IRIX tar is inadequate as is. 

There's a few options we have to replacing it; all with benefits, drawbacks and often serious problems, as well as one option that while possible, carries legal risks. 

star - Schily Tar, a derivative of solaris tar. 
Benefits: Supports compression for gz, bz2 and xz, solving most of our immediate concerns, and presumably more sysv compliant. 
Drawbacks: Wasn't able to get it compiled to test for inst, am asking on their mailing list for help. Depends on schily make, which also is having compilation issues. 

libarchive tar - FreeBSD Tar and library. 
Benefits: Incredibly flexible, well-documented and covers pretty much everything include zip and CPIO files. 
Drawbacks: Dozens of deps, latest version doesn't compile (3.3.2 is the latest I got to work), and last time I tried, over a year ago, inst didn't like it. 

GNU tar - GNU Tar
Benefits: Everyone knows GNU tar. It's also reasonably portable. 
Drawbacks: GPLv3, doesn't work with inst, bloated and slow, poor documentation and highly obfuscated. 

And finally, I do actually know where I can get the IRIX tar source. I also know it's based on 1980s BSD tar. I also definitely did not peek at it and confirm it was about 400 lines of code. But of course, modding the code and opening one's self up to legal liability is a huge risk. And while there's a few approaches to solving the "no compression support" issue, the one I was thinking of if someone were to take this route is:

Have it check the extension of the file, and call the appropriate program to uncompress, and then untar it as normal. 

My .02: I don't want to Linuxify IRIX. this is why I have looked at replacements for stuff like libtool, and getting around stuff like bash, gnu tar etc. I'm always willing to put money and my own two hands down to avoid that conclusion, but I guess I'm alone there? I would almost prefer if IRIX were to remain proprietary than for it to be mostly GPL and be released and turned into a monstrosity of Linux-derived code and tools.