One of the most interesting "experiments" IMO was when they tried to put Kikaider into the Metal Hero universe in form of Metalder.
I never understood why they didn't just do that from the beginning.
Like Ultraman, people in Japan STILL recognizes Kikaider, and he has appeared in various KR and SS stage shows, and now in the latest All Rider movie as well.
As much as I love the police-themed MH shows, I think perhaps the Metalder route could be the best way to go. They just need to make it a new Kikaider series (actually USING the name), and we are ready to go.