From this kind of response, it's always so hard to tell whether it's easy for you because you have the relevant experience, or you just think it's easy because you don't.

A (very non-exhaustive) list of interesting questions about IR design are:

* What's your model for delayed UB and UB materialization?

* What's your provenance model?

* What's your strategy for information retention and handling of flow-sensitive facts?

* What inherent canonicality is there?

* What's your approach to target or domain specific extensions?

* What is your strategy for formal verification of refinements?

Questions like "What instructions does your IR support?" are fairly uninteresting, and are not what IR design is (mostly) about.

It's worth noting that LLVM's own IR design doesn't have a very good answer to some of those questions either, in part because making changes to an IR that is as widely used as LLVM IR is hard (been there, done that). It's easier to design a new IR than to change an existing one -- however, unless you just want to reinvent past mistakes, it is certainly helpful to have deep familiarity with an existing IR design and its problems.