I have access to Lightroom through CC and I'd like to use it more, but it cannot do a very basic thing that Photoshop Elements, a consumer-oriented product, has been doing for years. That is, stack across different folders. I keep my large RAW files on an external hard drive but keep the edited .jpg files on my computer's main drive. In the Elements library I stack those photos and any other versions such as .psd files. Very useful and I don't understand why this has never been possible in Lightroom.
An additional wish is that I could import my Elements library into Lightroom, complete with stacking, keywords, etc. That would be fantastic.