Couple of things for you.
In lightroom (just tried on 2.4) you can drop into an impromptu slideshow and flag your pictures as they go through (p for pick, x for reject). This is a full screen slideshow and can be started with the shortcut (cntl+enter (on PC at least though can start it from window menu)).
Personally I go full screen lights out as you do (short cut cntl+shift+tab or cntl+shift+f will go full screen in one go then L,L for lightsout). Then use capital P or X to flag as picked or rejected. Because it is capital (ie caps lock) it will automatically move onto the next photo once you have picked or rejected it. I find that better paced than waiting for a slideshow myself.
Obviously this doesn't help for keywording...
But the keywording stuff sounds very achievable using the painter in library grid - set your paint keyword first and then just click the keyword into each image in place of selecting it as you did in your old work flow. Or in library grid mode select all the photos you want to add a keyword (or make a rating, metadata change etc.) click on the paint icon on the grid tool bar (make sure it has been set to be visible from the toolbar options), set the keyword you want to add to those images and then click on one of the selected images and all of them have that keyword (also works in grid mode if you have them selected and then just add the keyword into the keyword area - it'll give you a selection of previous ones.) The painter also lets you wizz over your images and painting inthat keyword or what ever at will - not quite the same as your old workflow but maybe useful for you.
EDIT 1 - Note bulk update of keywords only works in library grid mode - that caught me out for a while.
EDIT 2 - Thinking about it - preselecting in library grid mode and making use of keyword sets gets pretty close to your old workflow - you don't drag the selected photos onto the keyword but once selected you can open up a keyword set (or from the list of used keywords) and just click on each you want to associate with the selected photos (keyword sets might make organising it faster.
#5965778, By Jos EG Gods of Lightroom, share thy wisdom
Jos 711 posts
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