not really related to: "Why in olden days was there a long break between Kiddushin & Nisuin?"
In the times of the Talmud (Ketubot 57a) there was usually a significant amount of time between kiddushin/erusin (betrothal) and nisuin (marriage).
However ever since the Middle Ages (source) the practice has been to do the kiddushin and nisuin one after the other under the chuppah.
When did this practice of doing Kiddushin followed immediately by Nisuin begin?
Do we have any teshuvos or documentation from the Rishonim as to when exactly and why this practice began?