I'm currently attempting to sync a full witness node on my system, and I'm at 54GB - and only synced up to mid-Nov. 2016.

I do think this will be a huge problem in the future, especially as people are pushing more content. It will be completely unsustainable if they want to put video in there. There's already very few witness nodes (less than 200?) which would seems like it could be a major problem for the network. I'm still figuring out DPOS based blockchains, so it could be perfectly secure with that low number of nodes - just seems odd to me.