It is perhaps difficult at times to track down the origin of wearable computing and/or its integration into fashion designs. One could make the argument that is began when people started hacking raspberry pi's with LED's and glueing them to ones shirt or further back by hacking Asus Eee and changing the location of it's screen on clothing. Jumping forward we equally have the competitors of the MIT's LilyPad and later AdaFruit's Flora, followed by their Gemma. Is conductive thread not equally as applicable as Silicone Cover Stranded-Core Wire in sewing wearables? I would say it is.
However these are arguments that have yet to become black or white as the entire wearable computing and wearable tech in fashion is still evolving and has only become better know since Apple's jump into the market with their Apple Watch; a mix of accessory fashion design, technology and bio-metrics. I personally believe that within 10 to 20 years wearable tech in all forms of clothing and fashion will become a reality, but time will tell.
AdaFruit has continued to become a major contender in development of wearable tech and sewable tech such as their Trinket and Sequins. While their are not a manufacture of wearable tech fashion design, their products do indeed help many with their work be it at agency level, corporate level and even DIY level, as the video below illustrates:
At agency level, Cutecircuit is producing experimental wearable computing in fashion and recently helped develop an interactive dress for Katy Perry. Further examples of their work can be seen below:
Even the level of DIY work has grown with the expanding accessibility to physical computing parts, cheaply priced textiles, e-textiles and ad-hoc usage of technology for other uses; such as the below video using fiber optics commonly used in telecommunication, now used in fashion design.