Easy importing of lessons from YouTube and Netflix, the built-in libraries of lessons, guidance on what content might be most appropriate to your current level based on known vocabulary, the mobile apps with playlists and audio player, things like that.

(Disclaimer: I haven't actually used LinguaCafe, but am a longtime LingQ user, so I'm not really making a fair comparison. I know LingQ's feature set much, much better.)

Last time I checked, it couldn’t handle expressions that are not just tokens one after the other. For example, German separable verbs. I tried fixing it here: https://news.ycombinator.com/item?id=38915786

Importing audio along with the text is a big one. Failing that some sort of TTS would be very useful.