I see it as a legitimate legality issue.
It's illegal to disable the DPF exhaust and keep it on the road. It is not as much of an issue with simply adding modified shift points or improving efficiency.
The question still remains "Does it work". If the results are going to be short lived before major DPF issues ensue then there is no point in doing it.
If however there was a complete system to replace the DPF with a larger one that actually works good and does not restrict the exhaust. Maybe a much larger one that gets regenerated by an external source other than by the engine and with it's own controller, disabling the engine regen all together. This would solve the regen problem with the 6.4L and remain street legal.