I think the software dimension adds some fuzziness to what can be considered a complete 'kit'. For instance, I've been able to piece together a voice assistant using a Matrix Creator [0] and a home alarm retrofit using Konnected [1] that is more tailored to my needs than any commercial offering could be. Both projects can be thought of as kits, but one can take any number of paths toward setting up and maintaining the software behind the system. Furthermore, the pace of development is so quick that a particular system may lose development interest to a newer sexier project, and if your system connects with third-party APIs, that is always a moving target.

So, I think the spirit of kits lives on, just in a different way :)

[0]: https://www.matrix.one/products/creator [1]: https://konnected.io/