It might be easier to build an export filter that combines the outlines from the two layers only on export. So you draw the bars in one layer and the circles in the other (you can make the other outlines visible in the layer panel).
@GeorgSeifert I’m also up for this feature. It would be very helpful in my projects. Here is how it would really improve my workflow:
I make layered colour fonts. Let’s take for example numbers and fractions. I have some design that uses two layers. Let’s call one of them “outline” (brown) and the other “small details” (orange), which is basically the same layer covering 90% of “outline”, but has some small cuts at the corners. I want my numbers to have those cuts, but I feel that I should not use them with fractions which are already small and it would only cause difficulties in reading. So I want the “small details” layer to be exactly the same as “outline” with these glyphs. Here adding a component from the lower layer would really come in useful.
Is this feature still not realized? It would really be very useful. For example, I have two different masters with alternate narrow and wide characters. Where one master has narrow alternate signs, the second master has wide alternate signs. We need “Cross Master Components”. At a time when the number of masters is increasing from font to font, the case for such a function is becoming more and more relevant.
@lettersign I agree, I would really use being able to use other glyphs as smart components, for example making small caps that are components from uppercase, scaled down, but at the same time a bit heavier to compensate for the weight loss after scaling down.