My take is,
MLIR is a replacement of HalideIR. 1) compiler infra support, like cfg/dfa/ssa, with these, we can avoid pattern matching style pass on Halide, which is not good for maintaining, 2) other better utilities, like text ir; 3) unified IR for multi-level, graph and tensor.
I agree the idea we have a MLIR phase in TVM. if it’s indeed better, we can move our work to MLIR gradually, or just write new optimization pass on MLIR.