I'm extremely tempted to play the moment the game downloads on steam but I know that if I do I will be disappointed, so I may as well wait...
Well, for most people there's only so much free gaming time available. For those that like turn-based RPGs, Wasteland 2 is coming out in two months, Blackguards 2 is in development, not to mention D:OS mods.. so I suspect everyone would prefer playing the main D:OS campaign sooner rather than later.
If the personalities and companions are showing up in a week or two, waiting isn't a big deal. But if we're talking about months of delay, then maybe delaying your playthrough of D:OS isn't the best idea (especially if you're interested in other games that are around the corner). You can even save the AI personalities and extra companions for a different playthrough experience your second time around (if you can honestly see yourself playing through D:OS twice).
I mentioned this before, but I'll say it again. As far as I know these are the available traits:
Pragmatic vs Romantic
Altruistic vs Egotistical
Independent vs Obedient
Righteous vs Renegade
Bold vs Timid
Compassionate vs Heartless
Forgiving vs Vindictive
Spiritual vs Materialistic
An AI personality is probably going to be made up of a single assigned traits from each of the above eight rows, which in turn will determine how your AI-controlled person responds during conversations.
If you really want to start playing on the 30th, you can just as easily pick the traits you best feel will make up your preferred personality for your partner rather than waiting for a developer to do it. And then you simply choose the appropriate responses for them during conversations rather than the AI doing it.
I know that despite the end result being the same, it won't feel (as when the AI does it), and it requires you to remain honest to your trait assignments. But for those who want the occasional conflict between their main characters and are desperate to start playing immediately, it's worth considering.
Or, just wait for the update to arrive. But the wait might be a while, and consider the possibility that there may be other things down the line you're going to want to play.
What's the point of ETA if it is not going to be kept? And if it is not kept, there are always some people who accuse the devs lied to them. They could give you a very rough schedule, which, however, can still be broken. At least, that's what I learned from following some game developing companies for these years. I even have never taken the day & night stretch goal seriously since it seems to end up with plenty of works, which could extend to various layers. As for the companion stretch goal, I imagine it would be basically adding extra content but the AI thingy can make it more complicated. So, I'd wait for it with a caution.
A safer way to give an ETA is to make it clear that a feature has no chance of appearing before a general date. As in
"No additional companions for at least two months". Even that vague answer can help people make informed decisions.