The GHC Steering Committee has been struggling recently to decide on several related proposals. The struggle is all around whether we should favor making a design that is future-compatible with dependent types, or favor a design that is more cohesive with e.g. Haskell98. (Sometimes, we can have both. Those are good times.) This isn't about backward compatibility -- the design for dependent Haskell is fully backward compatible with Haskell98. It's more about how well the new features fit with the old ones.
To clarify our thinking on it all, I've made a new proposal to discuss whether or not we want to favor keeping an avenue open to ergonomic dependent types in the future. If you have an opinion, please express it on the proposal. In particular, if you care about the possibility of ergonomic dependent types in Haskell, now is the time to show that support by thumbs-upping the proposal.