I tried something similar to this, but I didn't like it. After using it for a bit, I realized I often use commands other than i to get into insert mode. For example, I may use ci" to edit everything inside a pair of quotation marks. I wrote a bit more about my setup here: https://jeffamcgee.com/using-a-vim-clutch.html
I have a 2016 MBP w/ touchbar, and depending on which color display profile I select in System Preferences, sometimes I can see it, and other times I can't.