The F2P model of KI is similar to DOA5 and was released afterwards (there's also free rotation there).
September 2018: F2P version is planned (release date unspecified) via Famitsu . Earliest mention I could find, but I'm sure there's more. There was an interview where he said it would come "soon after launch", but you'd excuse me for not having the time to look through plenty of japanese websites and links right now.
If you have the time, feel free to do it. Again, it's the same model as DOA5, so not surprising it's that soon (especially when they made most of their profits through that and when they made most of their DOA5 marketing through that as well).