It is indeed early to say, but the design of the compiler pipeline is very different to rustc, it is a more traditional pass based system with plenty of side table lookups. Some of the notions are similar we are using HIR but we are not using MIR, GCC's generic IR is very similar.
So we have
AST->HIR->GCC-Generic->GCC
where as rustc is:
AST->HIR->THIR->MIR->LLVM-IR->LLVM
So we have AST->HIR->GCC-Generic->GCC
where as rustc is: AST->HIR->THIR->MIR->LLVM-IR->LLVM