waiting on

The use of "wait on" in the context you describe is quite common in Scotland and, I am given to understand, in the southern states of the USA.
I'm not sure in which other regions it might be common, but its usage does seem to have become acceptable.
Purists and pedants may cringe but common usage will always be the final arbiter.
While I rarely use the phrase, I see nothing wrong in its use as an alternative to "wait for".

HS got there before me. Yes, you hear it quite a lot in Scotland - "I'm just waiting on my friends". I was going to suggest it was more colloquial than standard, but then I found this on the official website of Edinburgh University:

"Those waiting on exam results will be sent offers once your exam results have been received by the University."

and this from Skills Development Scotland ("a public body", i.e. a quango)

"Waiting on Exam Results - Don't Panic"

It's also crept south of the border. This is from The Telegraph

"Liverpool news: Jordan Henderson waiting on results from scan on injured foot"

And from the Scottish press:

(Alistair) Darling: World is waiting on currency answers - The Scotsman
Horse Racing: Sprint boss waiting on course thaw - The Scotsman
Cold comfort for patients waiting on operations - The Herald

But there aren't too many, and this one from the Herald suggests the writer perhaps wouldn't use the expression himself - ' He said the advisory group was "still waiting on an answer" from the industry on the question of an alternative to strict liability.'

Some are a bit ambiguous. This is from the BBC, but does the "on" belong more with "waiting" or "deals"?:

"Crewe Alexandra: Steve Davis waiting on two defender deals"

A couple from the British Parliament:

"but they have always seemed to be waiting on a decision from others in order to be able to allocate time."

"Q7 Jeff Cuthbert: So, Arriva Trains is just waiting on a decision from the Welsh Assembly Government. Is that what you are telling us?"

Does it have a special affinity with words like "results" and "decision" in these more standard English contexts, I wonder?

In the US saying waiting on sort of pegs you as a southerner, almost as strongly as y'all. Ahm waitin on ya means hurry the heck up.

I don't know if this really helps, but just for this example alone I would interpret "waiting on your mother" to mean the rest of the family is ready to depart for somewhere and she's holding up the group while "waiting for your mother" would mean she has not yet arrived where the others are located. (I'm from Michigan, for what it's worth.)