I like the white ceilings but painting the stone was a dreadful mistake. If there was any way to sandblast that off I would start there.

I agree with Hallett, the stone looks bad. Maybe you can cover it with woodwork? Sandblasting it would be a really messy job, and you don't know what the stone will look like after all that work.

What does the rest of the room look like?

White actually makes the space look small and constricted. It's going to be a job to get the paint off the stone but it will probably be worth it.

Redo the fireplace. The white wood on ceiling and fireplace looks to be shrunken up and may be in poor condition- that might be why they painted it.

You could honor the spirit of the A-frame but go ahead with a new fireplace and insulate the ceiling, then install wallboard and paint.