Sure. I'm not saying it's impossible to construct such an IR and get it to work, I'm saying I doubt it's the best way forward. See my other comment [0] where I mention Google Native Client.
It would be a poor fit for certain languages, there may be performance penalties depending on target platform, it would preclude legitimate platform-specific code such as SIMD assembly, it would preclude platform-specific build-time customization, etc.
The way toward painless portability is to move away from unsafe languages like C and C++, where you're never more than an expression away from undefined behaviour, and where programmers may be tempted to make silly mistakes like writing code sensitive to the endianness of the target architecture. [1] With C and C++, disciplined developers working carefully, can write portable code. With Safe Rust, code can be pretty close to 'portable by construction', like Java. If you feed Windows-style path strings to Linux, or vice versa, then things might go wrong, but for the most part you'll be on solid ground.
[0] https://news.ycombinator.com/item?id=26398199
[1] https://commandcenter.blogspot.com/2012/04/byte-order-fallac...
