Copper Fox and TeckTeck has a lot on their plate with what they already have. Let's not forget that they're big in three areas: copper, metallurgical coal, and zinc and want to get bigger an all three over the course of a few more years. With the capex. and other costs it's really going to cost them and it's not something that they can put off, or put off indefinitely.
Their acquisition of Fording coal was an eye-opener on how fast things can change from great acquisition to crippling them for several months. Their debt levels are good now but they're not soon going to forget what happened just a few years ago. I believe Teck will wait for the BFS until they make their move to either back-in or buy them out completely. I'm thinking the former at 75% and spinning off perhaps 25% for a huge premium. That way they're eventually "paid" to back-in.
One way to change this scenario is to have a buyout by any company, including Teck, before CUU completes their BFS. Then maybe a bidding war???
IMHO once the BFS is complete, Teck WILL act.
Chris