If we all agree that right now (beginning of 2017) iron ore...

If we all agree that right now (beginning of 2017) iron ore supply and demand are net net the same (i.e. the new supply added by Roy Hill last year has already been aborbed) -

Then this year:
- ~25Mt from Roy Hill
- ~30Mt from S11D
= total of ~55Mt new supply for 2017

2018:
- ~30Mt from S11D
(S11D will probably add another 15-20Mt in 2019 and the last bits in 2020)

If we really try to be more specific:
- Silvergrass from Rio, which has capacity of 10Mtpa (starting late 2018 or 2019) if it gets approved and goes ahead
http://www.riotinto.com/media/media-releases-237_17773.aspx
- Sino Iron is probably never going to happen

I don't see any other new project (>10Mtpa capacity) in the horizon for the next few years.

So assuming everything holds the same (even without additional demand from US), then the key variable here is how much China cuts domestic iron ore production.