New frontend is still unstable:
1. It has some bugs so correct code can be analysed incorrectly (but correctness now ~99.98%)
2. There are no a lot of diagnostics except the base on produced by resolve and inference (type mismatch, unresolved reference, ambiguity)
3. Converter from frontend IR (it's a main structure used by new frontend) to backend IR done only for 75%
4. Extensions for compiler plugins and services for such tools that you're creating also not ready
Summarizing, you can play with new frontend in compiler fork, but it's far away from using in real tools