Agreed, we actually have a Lua-5.2 frontend underway. We may officially support Lua in the future, but for now, we need to support full r7rs in Scheme.
I am glad you have picked up the embedded functional flame. I assume when you say R7RS, you mean R7RS Small [1], Shen [2] might be a better fit for embedded dev as it is typed and has multiple backends including Scheme [3]
I think things get interesting when we have a core or more per pin and hardware GC.