We have three modern replicas of vintage grail items to date. They are the Rocket Firing Boba Fett, POTF Yak Face and the upcoming Droids Boba Fett. I personally think this subset is one of the more exciting things to collect, especially for carded collectors. Due to the price and the prospect of yellowing bubbles (or other conditions that can degrade), owning the actual vintage items isn't for me. I'd much rather have the modern replica that I can get for a reasonable price, and if something catastrophic happens to it, I'm not out thousands of dollars. That being said, here are some ways the vintage grail subset can continue:
Vinyl Caped Jawa
When the original 12 Kenner figures were released, consumers scoffed at having to pay full price for the diminutive Jawa figure. To give the figure greater perceived value, Kenner switched the vinyl cape for a soft goods one relatively early in the production. "Vinyl caped Jawa" became an eponym for any scarce collectible.
Challenges: This modern grail would make zero sense in the Vintage Collection. Simply adding a vinyl cape to any of the modern Jawa figures would be anachronistic for lack of a better word. This figure would be much better suited to the Retro Collection. If Hasbro ever gets around to making a Retro Jawa, a convention (or other) exclusive with a vinyl cape would be the way to go.
Blue Snaggletooth
When Kenner was making the Snaggletooth figure for the Sears Cantina Adventure Set, they were working off of a black and white half body set photograph, and made a trifecta of mistaken assumptions. Kenner made the figure blue, tall and wearing silver moon boots. By the time time the figure was released on a single card, it was corrected to the short, red-uniformed version which is much more common that its Sears counterpart.
Challenges: Prior to its canonization in The Clone Wars, the character of Blue Snaggletooth didn't exist, and there is no realistic representation of the character. This would present a challenge for creating the Vintage Collection card, but it's clearly something within the capabilities of Hasbro's graphic artists. Additionally, to be as accurate as possible to the Kenner variation, it should be a blue version of the Holiday Special Zutmore, which doesn't yet exist in the Vintage Collection.
Glasslite Vlix
Vlix was scheduled for release in the second series of Kenner Droids figures, but the line was canceled before it ever saw production. The company Glasslite was producing Droids figures for the Brazilian market on a line-wide generic card. Despite the cancelation of the line by Kenner, some samples of the Glasslite version made it out to the market. According to The Star Wars Collector Archive, Vlix is the rarest commercially produced Star Wars figure ever (source).
Challenges: There are many. First, Vlix would require all new tooling, so this is an immediate nonstarter. Second, I'm sure that Hasbro has no rights to the Glasslite logo, so making a true reproduction would be impossible. Hasbro would have to retcon a US card. This is not unprecedented as Hasbro has retconned episode based cards for the vintage POTF releases, but as stated earlier this one is not happening due to the tooling requirements.
Of course, there is at least one more vintage grail that I've left off the list. It's the POTF Anakin Skywalker because that one comes with a question. Should it be a "spirit" figure or a flesh and blood middle aged Anakin (which never existed)?