Flash is much less powerful than DirectX. You would notice a massive difference in performance if it were possible to directly port a Construct game to flash. What's needed is a specialized runtime which limits a lot of editor options, since flash is not compatible with a lot of Construct's current runtime features(this will happen with Construct 2, but it won't use flash initially, someone will have to write a runtime for it. It might not happen at all.). Stencyl is a lot like construct, and it exports flash games. The difference in performance is massive. Massively bad.