Syntax is not the reason why the feature is in limbo (also there’s no conflict with struct literals in the current grammar).
The reason is that the feature is under-implemented (coercions) and is not generally useful enough.
Implementing coercions (while keeping soundness) will certainly move the feature closer to the final decision.
Implementing type ascriptions in patterns as an experiment on nightly will also move things in the right direction, I think.
Sources: