Don't worry. Because of the cap and the Coil reset, SE knew exactly how many lvl 90 pieces people outside of Coil would be able to obtain and probably took this into account. Not only this, the people who are actually getting BCoB drops is like 1% of the population.
Crystal Tower will likely drop myth tokens. It's supposed to be a step-stool to Binding Coil so the drops will be valuable. This will make it very attractive to everyone. It won't be obselete. :)
