Small gap. PM is a very good program with a strong focus on its small segment of the market. If Adobe did choose to go for that group, just how many features would they need to copy (stationery?) and how many loyal PM users would they gain? Would these be incremental users to Lr? Worthwhie?
There are a couple of different issues in what you say. Your tagged images requirement could be handled by a script. Have you tried writing or sourcing one? If not, why not, and what does that say about the wider need? Maybe I'll look again at my Locktastic plugin - I know I could now get it to import only those read only files, at least from the hard drive.
Update: I just looked at Locktastic again, and I had forgotten that the plugin does already import files marked as read-only, if that's how your camera tags pictures. So you can copy using the OS from the card to the hard drive, then use the plugin to pull those images into Lightroom. I've not tested it on a card, and think there would be a problem there, but I may be able to modify it to do so. You could then import from the card later, and bring in all its contents - Lr's duplicates control should kick in too. /Update
The other requirement is culling during Import. I have plenty of sympathy with high volume needs, experiencing them myself for periods and working closely with people who do so, though it tends to be in fields where PM is useless because of its inability to adjust (so much for Rory speaking for "any volume shooter") and where deadlines aren't too tight for Lightroom. I've said more than once that I would love a GPU-powered review of embedded previews, but in Library.
Locktastic is an option except for one small problem ... you have to use another option (workaround) to get there. Workarounds really aren't solutions ... just more work. Not to mention, it does not remove the task of getting the image onto the HD so the plugin can see them.
I pay Adobe to furnish me with software solutions to ease my daily tasks ... and they actually want to receive a monetary reward for what they provide to me for as long as I breath air (and longer if I should expire before my annual agreement does) ...
I continue to pay for PV2012 ... which I already paid for ... in 2012. I have paid for a Book module I can't use because I use vendors that have different page sizes, margins and bleeds than does Blurb and Adobe in all their wisdom doesn't think I am worth the effort to allow customization of same.
I also pay for a Maps module I do not need or use. I have paid for a facial recognition module I don't really need and I have been paying for a nearly useless Web module since it's inception.
Not once have I ever complained about the creation of. or the continued development of these modules (expect for my well documented complaints about hamstringing the Book module) or lobbied against their development or inclusion as I know there are many other users who do find value in them.
Why is it too much to ask for a few lines of code to assist me, and while a niche group, more than a few other like-minded Lr users, to have the ability to import only locked images? How many lines of code and how many years would it take Adobe to develop the feature? Heck, I was able to do this 5 years ago in Aperture without issue? If Apple could accomplish the task, how difficult must it be to offer? Why is it too complicated or unreasonable to ask my software provider of choice to serve my needs?
Sure I can see Adobe telling me I'm not worth the effort ... in fact not only are they going to ignore my request ... they would like to enhance my workflow further by stripping even more functionality I paid for without notice as a bonus. Just to please an unproven market segment that has yet to invest one single dime into Adobe's efforts. What I don't understand is my fellow user(s) lobbying against my idea and spend so much time trying to convince me how insignificant my concerns are?