Using source state in layer expressions

Motivation

I have a circle layer with an interpolation for the color property:

paint: {
	'circle-radius': ['case', ['boolean', ['feature-state', 'hover'], false], 6, 4],
	'circle-color': [
		'interpolate',
		['linear'],
		['get', propName],
		propRange.min,
		'#00FF00',
		propRange.min + propRange.range / 2,
		'#FFFF00',
		propRange.max,
		'#FF0000',
	],
	...
}

I want this interpolation to be relative to the minimum and maximum values of some dynamically chosen property of a geojson feature collection.

Design Alternatives

Something akin to feature state, but more like "source-state" that is usable in expressions would be great. This interpolation only needs to recalculate when my geojson feature collection changes (which happens as I move the map), or when the user chooses a new property to visualize with interpolated colors. I'd love to use this "source-state" concept as follows:

paint: {
	'circle-radius': ['case', ['boolean', ['feature-state', 'hover'], false], 6, 4],
	'circle-color': [
		'interpolate',
		['linear'],
		['get', ['source-state', 'interpolateBy']],
		['source-state', 'min'],
		'#00FF00',
		['+', ['source-state', 'min'], ['/', ['source-state', 'range'], 2]]
		'#FFFF00',
		['source-state', 'max'],
		'#FF0000',
	],
	...
}

const onUpdateFeatures = newFeatures => {
	source.setData(newFeatures);
	const { interpolateBy } = mapInstance.getSourceState(source);
	const { min, max, range } = findRange(newFeatures, interpolateBy);
	mapInstance.setSourceState(source, { min, max, range });
};

const onChangeProp = newPropName => {
	const { min, max, range } = findRange(newFeatures, newPropName);
	mapInstance.setSourceState(source, { min, max, range, interpolateBy: newPropName });
};

Design

The above design fits nicely in with "feature-state" in terms of usage and api etc. I am not familiar enough with mapbox's innards to know how difficult this implementation is or to really provide an example implementation.

The issue names no implementation file or test; begin by tracing the existing feature-state expression handling and the source.setData API in mapbox-gl-js. Determine whether source-level state can be exposed to expressions, then define the API and verify interpolation updates when source data or the selected property changes.