I don't think haki suits Franky. What I want to see is seastone gear. Hardest metal known so far, disables DF users (including logias), Vegapunk uses it, Franky studied Vegapunks stuff etc. It would be awkward if he would not use it. He also doesn't need to protect himself because his body is already tank'ish.
For Robin I could see dodge haki working, since getting hit is her only weak spot. Same goes for Nami, and her weird ability to "sense" weather changes could be a hint.
As for Chopper / Brook / Usopp….not sure. Armor haki seems to be necessary by the end of the series, tho Brook and Usopp could compensate with their own unique abilities - which could turn into anything as their strength progresses.
Franky maybe a cyborg, but he is still human or part human. Haki does not make one invincible, but it does help out a lot in tricky situations. I am pretty sure all of them will have haki, at some point.
I am not sure about the seastone gear, cause if thats possible, then why not give zoro seastone sword as well. There were some people who wanted that for zoro. Also, it does not seem all that great anyway, cause we haven't seen anyone except smoker use it, and even then it was not enough to achieve a victory. Haki seems more useful in a battle, imo.
And haki is something that everyone has available, they only have to awaken it. It does seem quite common in the NW.