What we are getting now, especially from Unity, are mostly art demos where everything the engine has is put together to make a super cool cutscene to use for marketing purposes regardless of the performance.
While I think this is correct and I do agree myself with the sentiment that these demos are not very representative nor illustrate what actual games will be like well enough, they are perfect equivalents to Agni's Phylosophy anf the Samaritan demo presented as examples in the threads opening post. So if the question is "where are these types of demos?" the recent U4 and Unity stuff is prety much the exact answer to it.