Why should they pay retail? As a consumer thinking about solar, I like that, but it makes no economical sense. What business can afford to buy and sell for the same price? You don't sell a car to the dealership for the price they will sell it for. That would be absurd.
If they are forced to buy the uncontrollably variable distributed solar energy, it will be at the expense of the peaking plant, and possibly even the baseload plant, if there is a large enough gap between peak solar production and peak energy consumption.
So it should pay, at most, the price it would have otherwise paid from the power plants if distributed small-time solar installations weren't forcing their excess production back onto the grid.
That means paying less than wholesale. So those solar installations end up paying a bit for the service of using the grid a like a storage battery--as they should.
If you're going to demand equal compensation for your solar power as the peaking power plant, you will have to install equipment on your end that allows the grid to control how much power it chooses to buy from you. Otherwise, it's like haggling over the price of a meal that is already eaten.
My guess is that they're going to compromise at around 75% of the difference between retail and wholesale. Nobody, except the power companies, really wants to see solar disappear, so the solar side is going to have more political might in this fight.
I get all of my energy from a roof top solar system but to stay on the grid I have to pay a connection fee which in my mind covers transmission costs and infrastructure. Being that it's a utility I can see them charging for that stuff, some how, either by a fee or by arbitrage between wholesale and retail costs, that seems reasonable. It radically changes the value of solar though.
If you can sell energy at wholesale prices what's the argument for restricting your ability to buy it at wholesale? Could you buy it from a different provider and just use the utility to transmit it?
Locally operated municipal utilities, however, are less likely to be turning a profit, at least not one that benefits shareholders.
Edit: clarifications
Obviously under completely free-market conditions, they wouldn't. But under those conditions, power companies would burn nothing but coal and nobody would have any solar. Coal is really cheap. Retail net metering is society actively meddling with the free market to mitigate a societal ill, and forcing big polluters to subsidize cleaner energy. I don't see a problem with that.