Good question. As Isan is where I spend my time when I'm in Thailand, and my wife is from there, I guess a lot of the food I see has got a typical Isan touch to it. To be clear, I lived a few years in Bangkok, years back, and I could not be too specific in what the differences are between Bangkok and Isan, whether street food or restaurant food. Then again, one has to realise that a good part of the food on offer in Bangkok is prepared by Isan people!
One thing I have noticed : I have nearly never seen people in Isan making the famous Thai curries (gaeng khiao waan or gaeng masaman for example), not even in the restaurants (maybe upscale restaurants do them). I might be wrong, and also that maybe is not unique to Isan.
As for food made in the houses themselves, what I have seen over many, many years now is that it is always the same few things. I do not see any interest whatsoever to look for new recipes (my wife being an exception). And I confess I end up being rather bored with it.
I'm sure other participants in the discussion can add much more to this.