We can “convert a normal paint layer to a watercolor … layer”:
1. If you have imagery on the Canvas, Select > All, then click inside the selection to lift it to a Layer.
2. Drop the “normal paint layer” to the Canvas.
3. In the Layers palette menu, choose Lift Canvas to Watercolor Layer.
4. Choose a Watercolor variant and Paper.
NOTE: In the next step, the Watercolor variant and Paper you’ve chosen will affect the result and it can be anything from subtle to extreme, depending on those choices. You’ll need to do some experimenting on a test image to learn which combination works best for you, in addition to any brush controls adjustments you make in the Water palette and in other palettes, and any adjustments you make in the Papers palette.
5. In the Layers palette menu, choose Wet Entire Watercolor Layer.
that would be pretty hip…
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also if there was a few more settings in the watercolour(imho should be color liquid simulator, because water is a dubset of that) like:
Another thing you can try on a Watercolor Layer is to choose a Watercolor variant and, in the Brush Controls’ Well palette, move the Resaturation slider to 0% and the Bleed slider to 100% to make it work like a dry media blender but instead work to “blend” and move existing Watercolor paint without adding color. You may want to tweak the Resat and Bleed slider settings to get a result you like (if you like the idea at all).
a) radial dispersion
b) liquid/pigment separation ratio
c) dryness/reactivation rate(the cool thing about xylene and this technique in my first post was that the xylene “dried” but you could rework it with another wet chart pak.
d) liquid/pigment density…chartpak grayscales had different densities of color…not colors chosen from a color wheel.
that is just for starters…
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BUT …
how could I take a hard media marker drawing and “easily” convert it to water media…at a highly workable resolution?
See steps to Lift Canvas to Watercolor Layer and Wet Entire Watercolor Layer above.
THANKS FOR AT LEAST PONDERING THIS WITH ME
Also, have you tried playing with the Brush Controls’ Liquid Ink palette settings? I’m thinking especially of the Ink Type list of options.
Now I’m wondering what can be done by making the finished Liquid Ink Layer your “paint layer”, dropping it to the Canvas, lifting it to a Watercolor Layer, then wetting the Watercolor Layer. I’m imagining one could get some interesting effects using this combination of media (Liquid Ink and Watercolor).
If I’m way off base here, just ignore me. 
Jinny