There are thinly veiled hints that there will be a way of outputting an HTML front-end from LightSwitch very soon. (Possibly by RTM of VS 11 ~Sept/Oct 2012.) Given that it is built using MVVM this shouldn't be that difficult.
Whether this will give the level of sophistication needed in the UI remains to be seen. It may be even more restrictive than the current browser-based Silverlight implementation which is too restrictive for some applications which must target the Out Of Browser Silverlight experience because they need access to the PC file system (for Export to Excel, etc).