P: Add a Multiple Exposure option to Photo Merge

You are correct.  Not HDR, not Panorama, and not HDR Panorama; but an additional Photo Merge option called Multiple Exposure.

The Multiple Exposure option would merge two or more photos (suggested maximum limit: three to five photos) using the blending modes as described in the link you provided. Those modes are generally referred to as Additive, Average, Bright, and Dark.

I don't know what post processing software may already have that capability.  I use Lightroom Classic exclusively, with an occasional edit in Photoshop.  I don't like going from Lightroom to Photoshop because I don't like having to save it back into Lr as a TIF file.  I wish Ps saved the image back to Lr as a DNG (but that's the subject of another suggestion).

To the best of my knowledge, a multiple exposure merge can be done in Photoshop, but it is a manual process.  Canon EOS cameras (and likely Nikon) provide the in-camera capability to merge multiple exposures, but you have to know which photos you want to merge beforehand and the process is a little cumbersome.

Having multiple exposure merge capability in Lr would allow the user to choose whichever photos he or she wanted for the merge (within the same folder), then select Photo Merge > Multiple Exposure.  Within the Multiple Exposure screen, there would be four merge options:  Additive, Average, Bright (or Light), and Dark.  In practice, this would be similar to how you have options for selecting different stitching perspectives in panorama merge.

I hope this additional information is helpful.

I assume you are referring to a concept/technique described in:

https://jmpeltier.com/multiple-exposure-blending-modes/

And not the common Merge Photo HDR.

You may want to expand upon that, and give more/better examples/references. And can you include any post processing software that has this capability in it as examples.