This is pretty cool but even when it is more robust and works with optimized code I think most developers looking for something like this are far more likely to choose LLVM for licensing reasons.
Current gcc is GPLv3 and that is very unlikely to change, if you link your project to this you are thoroughly "infected" by the GPL since unlike many GNU projects that are explicitly meant to be linked to by your own projects, gcc's core is not LGPL and the runtime library exemption granted by gcc is not sufficient to save you from infection in this use case.
Unless you are extending the compiler why would you care? GCC consistently produced faster code that LLVM
If you are extending the compiler, why would you want to allow companies like apple and oracle to bottle up you hard work and not give anything back? Either by not giving the code back or by patenting parts of the functionality they add and then suing you when you try and use them.
And? The above post asks why companies need to make proprietary code changes to the compiler, or why the community should allow distributors of GCC to patent parts of the compiler and then go suing users who the distributer gave copies to.
Even if you don't make changes to the compiler, if you link to this project you are GPLv3 infected. You simply can't use this without exposing your entire project to GPLv3 infection, the usual LGPL and/or runtime library exceptions don't apply to gcc's core code because it was never intended to be used as a library.
Let's say you have an existing FOSS app that is BSD or MIT licensed and it has its own built-in scripting language. You'd like to build a JIT for that scripting language, you see this library and decide to use it in your project, well... you can't do that without changing your entire project to GPLv3 terms because the combined work created between this and your own code all has to be available under the GPLv3 terms. This is usually solved by making the relevant parts of the project LGPL or granting a runtime library exception but neither of those applies to the core gcc code, so the GPLv3 infection in unavoidable.
Whether or not that issue is important is open to debate and depends upon your software politics, but in practical terms it means very few people will use this in their project unless they are already GPLv3 committed for some reason.
Current gcc is GPLv3 and that is very unlikely to change, if you link your project to this you are thoroughly "infected" by the GPL since unlike many GNU projects that are explicitly meant to be linked to by your own projects, gcc's core is not LGPL and the runtime library exemption granted by gcc is not sufficient to save you from infection in this use case.