I think the $20 price (giving a $1B marketcap to LTC) will be a good test point.
As if it breaks through $20, it could go to $40 too, testing $2B marketcap. ETH has $4B, so it's possible.
All of this depends on BTC scaling up development too of course.
But I like what Charlie Lee wrote in his blog post on SegWit for LTC and BTC, saying that even if BTC implements SegWit, it won't be able to process all the world transactions at some point and will need its beloved punching bag sister coin