Tron

I just mentioned alpha blending as example, which is already there and uses paletted input data (actually one paletted pixel + one direct colour pixel get blended), but produces direct colour as result. Colour interpolation for resizing uses pretty much the same calculations as alpha blending.

I will stay by my statement that blending and resizing are essentially different. You can implement it so that they look similar, but the essential operations do not overlap.

The essence of blending is being able to read a WRITE buffer, that is read a pixel from the WRITE or FRAME buffer, blend it with another pixel and finally write it again into the buffer. Where the other pixel comes from, being it a rgb or paletted source, doesn't matter. The essence of resizing is the computation of one new pixel from one or several source pixels. The way how you compute/interpolate the new pixel determines its quality and what you finally do with it, write it directly into a buffer or use it as input for a blending operation, again doesn't matter.
Now, you can nicely chain these operations, but on an essential level they have nothing to do with each other.