Conceptually, Google Photos is very much a V1 product. It might sound a little weird since the team is experienced and a lot of the technology it is built on has been through multiple iterations.
But from a _product perspective_ Google Photos is a new product.
The product team was really focused on a few key aspects of the user experience (I'm not going to try to enumerate them here. The main reason is that I would certainly do a poor job of explaining them. The other reasons are that I can't remember how much of the strategy has been talked about publicly and it doesn't really matter for the point I'm trying to make).
Being focused meant saying no to things - at least for the initial launch.
So the first answer to your question is that for most of the mentioned features the answer is that they simply didn't make the cut for V1. I can't comment on which features will or won't make it to future versions.
Date picker is an interesting one. Really, the only reason it existed was to work around how painful it was access older pictures in Google+ Photos, Date picker was added to (somewhat) ease that pain.
In building a new product, there was a desire to make things like date-picker unnecessary. Make finding older photos so fast and painless that you don't even need it. Try grabbing the scroll bar in the new web-app - you can scroll to any time you want in seconds. On mobile, it's easy to zoom out, scroll and zoom back in.
There is also search, which often means you don't even _need_ to scroll through your photos to find what you want. Just this morning my wife wanted me to find a picture of a tatoo from six years ago. I was able to find it by searching for tatoo. It was awesome! In Google+ Photos I would have spent a long time trying to figure out the right date range and then searching around.
If you really want to jump to a date, just type it in search - I just tried "September 2012" and "9/23/2012" and they both worked great.
So I would argue that date-picker just flat out isn't needed any more, because the team focused on some core user experience flows.
Still, I find it kinda weird that Google feel the need to reinvent the wheel and redesign the whole site from scratch, when the old Google+ Photos is generally considered to be very well built. Why can't you just take Google+ Photos front end and build it up from there?