If you want backwards compatibility I think it really makes more sense to target LuaJIT. It runs on *most* of the devices where you'd want to use Lua and Mike has been reluctant in the past to break backwards compatibility regarding things he thought were unnecessary. If people want to build a Lua module ecosystem, LuaJIT appears to be a more attractive/stable starting point than any point-release of Lua, plus it's fast enough to compete with Java and trounces V8.
The Lua interpreter is really awesome in embedded applications -- for video games, automobile HUD systems, NetBSD kernel "scripting", various Cisco products, etc -- none of that would be inhibited in any way by the standalone webapp and desktop people targeting their tangle of toolkits and libraries to LuaJIT's dialect and header files. It worked well for
http://torch.ch/ after all.
