They claimed no webgl support when someone asked about it.
Without webgl, it will use canvas2d, which is still hardware accelerated, even if it's not as fast as webgl. Software rendering only happens on browsers when the graphics card is blacklisted, and I'm pretty sure nintendo's not going to blacklist their own card. :)
Aside from no shaders the main concern I have is the lack of layout by layout loading, meaning the entire decompressed game has to fit in the available memory - or hope that nintendo's own memory management is up to the task of sorting it all out.