I think there will be a decline, but even if not there will be a shift. In particular, high-grade cards and pricing will change.
I mean, what is the percentage of high grade Pre-War cards in holders that are altered? 50%? More? I don't know, though my guess would be more. People may still want and collect and pay fair money for these cards, even if they know they might be altered, but someone would have to be either entirely ignorant or brain dead to pay the same premium as before-- especially considering many of these altered cards are being exposed daily and, upon exposure, their value drops by, what?, a factor of 50 in one second. I suspect this will also happen with modern cards, even today's. And I expect a sizable enough number of collectors to leave that market altogether.
"What would I pay for a really good looking card that has been altered or restored and would be labeled as such?" That's how many will start pricing high-grade cards.
As I've regularly said, it doesn't take everyone changing their pricing considerations and collecting habits to shift the market, just a sizable percentage. That there are some "Registry holdouts" is neither here nor there.
In the future, cards clearly identified and identifiable as unaltered may get big premiums. This may happen in today's cards and inserts, where box breaks are filmed live. Put the card directly in a holder with tamper-evident seal, photograph it and send it to PSA or whomever.
Butt of many This is Spinal Tap jokes originally, but SCDAuthentic had a Grade 11 for cards that came directly from packs.
And once there are sales of sets or collections, or even single cards, that have been prominently advertised to be "proven to be unaltered" and/or "rare and highest graded proven unaltered cards," that will definitely catch some hobby collecting awareness. All those unproven to be unaltered PSs 9s and 10s in PSA holders may suddenly be considered by the hobby to be "nice but second tier" in the collecting echelon. Wouldn't be surprised if PSA and SGC come out with a "Straight from pack" designation for their holders.
I promise you that once a big auction house or eBay seller offered a prominently advertised and noticed sale of high graded and graded "known to be unaltered cards" (ala documented as straight from packs, or otherwise shown), it will change collecting minds and tastes. Once collectors boast, as they like to, about owning the "highest graded proven to be unaltered" card or set, hobby minds and tastes will change.
I think BO's exposure should continue forever, because it keeps the hobby honest and aware, and gives sanity and common sense to people buying potentially altered cards. As I said elsewhere, BO and others exposing misidentifications, alterations and misgrades are part of the grading. Obviously, PSA is unable and/or unwilling to proper authentication and grading on their own. In the area of highest grade Pre-War cards, their error rate may prove to be higher than 50%. Which, if that is the case, common sense and anyone who got a C- or above in middle school Logic for Dummies class would tell a collector to go by the opposite of their opinion because the complete opposite is more likely to be correct. Heck, I think even someone who got a D and skipped half the classes could figure out that one.
And, considering the PR releases and intuitional stance that people should ignore it and quit whining and that it's not an issue of concern for them and their stockholders and at times throwing up their hands and saying "What do you expect from us?" and only addressing cards that are officially outed and choosing not to remove outed cards from their database, a question to ask is if they are even attempting to correctly grade cards? At this point, is correctly labeled cards even a concern, or their main concern? If it is, they'd better do a better job of demonstrating it. As far as I saw, Joe O's letter's stated "We don't know how to do it, so get over it." Even PSA forum members were shocked and disappointed at that response. One said that at the very least it was tone-deaf to the concerns of their customers.
It's pretty obvious that PSA doesn't want to correctly grade all the cards out there. They want to have a way they can avoid doing it. And, again, even that D middle school student who skipped half the classes can see that "We are a company that correctly grades your cards" and "We are a company trying to avoid assigning correct grades to cards" are at odds with each other.
And even that very mentality existing in their grading model should point to a company you don't rely on for correct grading. Forget the issue of if they can do it, because they don't even want to do it. Their PR statements and actions actually say "Our business model is that we don't want to have to correctly grade all those cards out there in holders. It would be against our business and grading model to have to correctly grade them."
PSA and their cadre of "Buy the label even though it's wrong" collectors has become the bizarro world of grading.
Seinfeld: Bizarro Jerry
Or, for an even better comparison,
Attorney Lionel Hutz in The Simpsons