† The qualifying clause is probably unnecessary here.
-Floating point math, not just integer
-Coprocess syntax that is correct and compliant
-Genuine Korn retains variables in control structures
-Lots more, detailed in the Korn & Bolsky ksh93 book
The language specification for ksh93 is large and powerful, and bash doesn't approach it.
cat file |\
while read stuff
do other stuff; set variable
done
In my experience replacing the build system and doing nothing else is usually a good indicator for a project that will be soon abandoned. If that's the first priority it means there's no real drive to implement anything new.
Have you actually tried the legacy build system before making that comment ? If not, I would suggest you to try that. It's by far the worst build system I ever dealt with. Just to give you an example, if there's a compilation failure in the middle of build process, build system will not stop, it will continue to compile everything that it should not compile and then exit with status 0. There was an absolute need to replace it with something newer.
Replacing the build system is just the first step towards improving the code base and it's not the end of it.
To the remark about build system, I would like to offer some speculation: I have (or had?) worked with its maintainer Kurtis by way of common employer on a few projects. He is a fantastic engineer and extremely careful and diligent; from that, I would grant significant deference. His team maintained one of the most sprawling pieces of legacy shell script infrastructure I have seen in my career.
Here's to hoping for a blossoming revival of the original essentials.