So, it's a small CLI tool that would be very useful for handling API responses such as Github API responses (which are JSON) in MiSTer scripts.jq is like sed for JSON data - you can use it to slice and filter and map and transform structured data with the same ease that sed, awk, grep and friends let you play with text.
The main advantages are that jq is much more robust and less error prone for its task, and is expected to be more performant in general. With it you don't need to build your own throwaway partial-JSON parser made with regexes, as jq has a fully conformant parser already built-in. jq should also perform better in theory, in both speed and memory usage, as it is tuned specifically for JSON parsing and querying. Plus, jq is commonly used in industry, and it's proven to be stable.
Main use for jq on MiSTer would be within the Updater. It would be used there to deal with Github API calls in a more robust and performant way. This would also help in a move towards using Github API instead of Github HTML pages whenever possible.
jq source can be downloaded from: https://stedolan.github.io/jq/download/
It has to be built from source for MiSTer Linux. According to that page, jq is written in C and has no runtime dependencies.