P: Alert/Show the user that multiple images will be affected during Develop

Thank you Califdan2 for pointing this out! I didn't know about this.    Yes, I see this as a cludge.  

1) I don't use the strip at the bottom.  I use a library view.

2) In both the strip and the library view it seems to hard to deselect the images, once they are selected in multiple.

3) It would be nice to have a warning, somewhere say up near the top, close to the image to say that you are affecting multiple images.

4) Right now this is a toggle switch which means that it presumes you want to set it as a mode of operation.  But in reality, during the workflow you want to sometimes edit a single photo and sometimes multiple photos.  This toggle would work AGAINST your wishes in both cases where  you do want to do multiple changes and where you don't want to do multiple changes, if you forget to toggle it properly at the time of the change.  

You have "Auto Sync" turned on in the Develop module.  Look at the bottom of the right panel group and you'll see that the left button is labeled "Auto Sync" and the button has a light background rather than the normal darker gray background.   That's your warning. click that button to toggle the mode back to applying edits to just the selected image. 

It took us several years of complaining to Adobe to at least get this much 'warning' which is light years better than what we had before which was nothing to alert you.  I would have preferred a flashing red button but it seems that a fair number of users who voiced an opinion keep that mode turned on all the time and are just careful with their image selection in the film strip and didn't want an annoying button constantly flashing at them.

BTW the Library module has similar "apply to all or just one" features which are a bit different but you asked about the develop module.