Does Android L Developer Preview fix the mm-qcamera-daemon problem? I have a Nexus 5 running on Android 4.4.4 Kitkat, and the mm-qcamera-daemon problem appeared today for the first time (I don't have the usual culprits like Snapchat or Skype).

Does Android L Developer Preview fix this issue?
Unfortunately I was still getting this issue (seems to come and go) under android L, so to answer your question, no, it's not fixed. 

See https://code.google.com/p/android/issues/detail?id=70755 for others who are reporting the issue still exists.