This would be super useful in both the Mobile app and the Beta site (10 points extra for the website, allows me to get spotify in work around all the security/admin nonsense)
Exactly what I am currently missing, I do a lot of travelling and mainly organize my playlists on my android devices, so not being able to add an entire album to an exisiting playlist ends up being quite annoying.
I'm practically an album-only listener. I don't care about single songs, so it's an absolute need for me (and speaking from an Android developer perspective, a ridiculous effort to integrate) to conveniently add a whole album to my current offline playlist. Please, make this happen soon.
I've just realised that this still hasn't been integrated. It would be extremely useful to be able to add albums to one playlist, instead of having 20 separate playlists.