I didn't know about QuickJS, last time I checked Duktape was most suitable for these cases. I see QuickJS was made by Fabrice Bellard himself. While linked benchmark is impressive for QuickJS, in case of Neovim they chose to embed LuaJIT which is ~10x faster than "official" PUC Lua. I see your point though, QuickJS would still be a good choice. JS and Lua are not that different once you set aside syntax differences.

http://luajit.org/performance_x86.html