I hate to bump something as old as this, but are there actually any plans to implement this? I hoped it would be in the official public release and was super pumped to upgrade my 1.4 Master Collection, but this really is holding me back.
This sprite is an example of something that I can easily work with in GMS but not GMS2:
The entire thing is made with just four shades of purple(and six pixels of black for the eyes), with varying amounts of alpha applied to the pixels in the middle to imply a membrane holding in fluid. While I was drawing it, and when I revise it in the future, it's easy to play with the shading on the membrane, the fluid levels, etc. by control-clicking to select a color then drawing with the blend mode set to replace. If I wanted to extend the shading on the upper-left corner of the membrane to imply more of a sphere, I could do it in two clicks.
In the GMS2 editor, I would need to erase the old color then draw in the new one, and that's if I only wanted to change one pixel and I knew exactly where I wanted to do it. If I wanted to mess with a lot of pixels and experiment to see what looked good, I could either: save all the transparent colors to a custom palette, replace the transparent colors with new opaque colors, draw my changes with the placeholder colors, then use the color change tool to switch back to the original palette and repeat until I got a result I was happy with, OR create an image with three layers, each one with a different level of opacity, which would still be difficult to manage because I would need to hit ctrl-z or erase and re-paint every time I accidentally painted on a pixel that already had color, and still wouldn't be quite right - the shading on the membrane isn't a transparent black applied to the original colors, which would be easy to accomplish with layers, it's from the bottom up the darkest purple, the medium purple, then the dark purple again with different alpha values, which helps accomplish a limited palette effect that's a snap in GMS but stupidly complicated in 2.
I know it sounds like nitpicky whining from someone who doesn't want to learn a new workflow, but I truly can't think of a good way to do the same work with GMS2 - If there is a good and convenient way to do what I'm talking about I'm happy to learn and try it. And the moment that blend/replace functionality is added to GMS2 I'll be spending a couple hundred bucks to upgrade, since I really like everything else about GMS2. But be honest: is there any plan to actually implement it, or not?