> How much of current carbon emissions are being factored into the cost of electricity (for any of the various sources)?
You can relatively easily do those calculations. The results are about what you'd expect: hydro, wind and solar don't get much more expensive; coal gets a lot more expensive, etc. Of course, details depend on what carbon pricing you use.
Funny enough, to go off on a tangent: if solar keeps getting cheaper and cheaper, that could make coal viable even with carbon costs fully priced in.
What I mean is: assume solar panels keep dropping in price so that electricity is approximately free when the sun is shining. But still has a very positive cost when the sun ain't shining. You can do some carry-over into the night with batteries, but seasonal storage all the way from summer to winter is much harder.
Now here's something that becomes feasible: when you have excess electricity from your solar panels, capture carbon from the atmosphere to build up a deficit. Then, when you need power but no sun, you can burn coal and use up your carbon deficit.
(I'm not suggesting this is in any way optimal, just that it might be feasible under certain circumstances; even if you fully account for carbon pricing.)