Continuous motion drills" (drills which are repeated indefinitely in a repeating cycle) and more especially "reciprocal continuous motion drills" (both partners doing the same thing in a continuous cycle) are very useful as a basis for spontaneously inserting techniques.
Used in this way they are fundamentally similar to "sensitivity drills" like Chi-Sau, Push-Hands, or Filipino Hubud-Lubud. Most martial artist understand this intuitively, and when engaging in informal partner practice they will often insert a technique or two into the drill. The partner of course tries to counter and the result is a brief exchange of technique before returning to the drill.
Pretty much everybody does this when doing -informal- kote-kitae/ude-tanren training. Unfortunately, this is rarely taught as a formal method and its full potential is never realized. Luckily, there are gifted karateka who do understand the potential that these drills offer as formal practice methods.
Here is a great example from Paul Enfiel shinshii of the Goju Karate Center:
Here is a video with Zenpo Shimabukuro, Dan Smith, and Arman (of the Kill Arman show) doing an Okinawan drill that can act both as a form of kote-kitae impact conditioning and as a kakie-like sensitivity drill. It is very popular on Okinawa and is extremely similar to a drill called "hubud lubud" in Filipino styles.
Here is a compilation video I created of various Okinawan continuous motion drills. These Okinawan drills can help develop sensitivity of touch and can provide a basic structure in which to practice close range techniques. Eventually, these drills can/should basically become a form of free-fighting done at close range (ie "trapping range").