I've seen smartphone games that are similar in size to the Monero blockchain, and people install those.
I'm not sure that running full node on a smartphone is what people will necessarily want to do, as other options exist with some partial privacy compromises, but if you really want to do it, the size of the blockchain doesn't get in the way really.
https://i.imgur.com/IaAEBYr.png?1
Case in point:)
The problem with deduplication is we sacrifice performance, which is critical on a smartphone...so the compromise will probably always tend towards less storage efficiency for the sake of performance. I'd be VERY interested to see how the lmdb-vl32 version performs on an ARM phone.
http://bgr.com/2015/03/19/samsung-galaxy-128gb-storage/