I suspect we can assume that Atronachs as golems have been completely and utterly retconned out of the setting, with the possible exception of the flesh ones, who, I get the impression, are still constructs, though I suppose they could have a Daedra bound to them, whether they've been combined with fire and ice Daedra or remain separate though, it's hard to same, but even if they look a little different, having two different varieties of elemental Daedra seems a little redundant, so I suspect that they are now the same.
As to their intelligence, there are several places in games where Atronachs have been shown to speak (In Morrowind, for example, one temple quest has you going to a shrine where three atronach's ask you riddles in order to test you.), that seems to make it pretty clear that they have a certain degree of intelligence, of course, the random enemy ones don't say anything to you, but neither did the random enemy Dremora in Morrowind, just because they don't talk (being as they're considered "creatures" instead of "humanoids", they don't have combat taunts, it would seem.) doesn't mean they don't have the intelligence to, it just means that they have nothing to say to you.
To your last point, you could also summon zombies, ghosts, fabricants, bears, centurion spheres, and bonelords, so we can be rid of the notion that summonability has any bearing on daedric matters.
It should be noted, however, that the fabricants, centurions, and bears seem to be limited to special spells, the list of commonly available summoning spells seems to be confined to Daedra and undead, Atronach's are obviously not undead (Maybe Flesh Atronachs could qualify as such, seeing as they're made out of flesh, but frost, flame or storm ones are certainly not.) they also tend to be encountered in places where other Daedra are, are referred to as Daedra by the lore, and, in the case of Oblivion, appear using the Daedra summoning effect if I remember correctly (As opposed to the one used for undead.) so it seems pretty obvious that yes, they are indeed Daedra.