@Elvin William
I think you will find that very little will change and the Seller will still pay the commission for both agents in the vast majority of transactions. Listing Agents will just not be allowed to advertise the co-broke that they are offering in the MLS, but they will still offer it most of the time, it just won't be advertised in the MLS. However, when they don't offer it or they offer something that is less than the Buyer's agent charges then the Buyer can just write in the offer that the Seller is to pay "x commission" to the buyer's agent. I have already seen the new forms/addendums that will be used here in Arizona, the common one for this will be the Seller Compensation Addendum.
The one thing that might happen in your discount buyer agent scenario is you might get a buyers agent who agrees to a lower commission and then the listing agent is offering a co-broke that is higher than he agreed to, well now that buyers agent will only be able to get paid the lower amount he agreed to and the listing agent will keep the remainder, so listing agents could end up getting paid more.
As far as your question on what to pay an agent, I view it similarly to hiring an attorney, there are discount attorney's and they might be okay for some people in some circumstances, or if you know the proper procedures and deadlines then maybe you do it on your own without an attorney. Or just hire the best and have the other side pay their fees for you.