MLPack has an existing ML framework, and now with each release, they are working towards optimizing their current algorithms like grid search and SGD, etc. Also, they plan to diversify their bindings in other languages like C#, Java, etc. and go for better parallelization.
So we can probably go ahead with integrating MLpack, and then with each release, it would be a task of code-maintenance.
Regarding the import and export of models, I am inclining towards export/import them as ONNX models as TVM stack is used for compiling and shipping models for hardware implementations.