I think using "to" or "towards" instead of "at" would be much simpler to implement and work as well as this proposal.

No special conditions are needed, those words work as well on complex ramps as they do in parking lots.

With Waze going to or at least playing with the idea of showing multiple directions when they are close together I can see it playing out on screen as:
Turn left in x feet
Then turn right at x feet
Then turn right at Waze Ave

That kind of thing will be helpful especially in larger malls / shopping areas.

My over-all suggestion for all cases:

1.) Next segment is named and the first word is NOT "to" - use "at"
2.) Next segment is named and the first work IS "to" - use "to"
3.) Next segment is un-named - use "to"

Case one is for most basic intersections.

Case two is mainly for ramps. I have a ramp signed in real life with a "to I-40" sign. This ramp leads to the last bit of another highway (which is not mentioned on any signs at that point) that splits to join each direction of I-40. I bugs me because you are in no way turing "at" I-40 and I use that ramp almost every time I leave my home.

Case 3 covers the parking lot situation as well as things like at-grade connectors where you are in effect turning BEFORE you reach the road and not AT it.

It may be the case where only the US is using "to" in ramp names, but these rules should then still apply to other locales I think.

PhantomSoul wrote:Beyond that, however, parking lot routes have very little use, as once you turn off the public road into a parking lot, you have to visually find your destination and just drive to it, since the entire parking lot, no matter how big, is typically defined as a single address, and the navigator will take you to the same spot no matter which store in that parking lot you might be looking for.

I agree with what you have said except a note about this part I quoted. That is true if you are searching for an address, but if you are searching by the name of a store it is possible that the search provider has returned a location right at the front door of the store.