I always understood that Stern doing Pulp Fiction was initially a response to Dutch Pinball doing The Big Lebowski. The rumors are that old. Prior to that, the theme would not even be considered suitable for them. For what it's worth, I also heard the game (read: playfield) was already designed years ago and not taken into production due to licensing issues and/or restrictions, which were already mentioned above. In order for the theme to work the game would have to feature songs from the soundtrack as well, adding more costs to it. I also read rumors that Quinten Tarantino would only allow a Pulp Fiction pinball machine if it would be an EM type of game, but I have no idea whether there is any truth to that.
Another rumor I heard was that a certain company was going after certain licenses just to prevent any competitors might get them. That could be one way of trying to defend your place in the industry, but also very expensive. At some point, the licensor will expect a game to be made. Taking a license just to get if of the market is usually not appreciated by licensors, although it was not uncommon in the music industry pre-2000. The difference is that record companies could license a track or album, release it in a small run to fulfill the license and then "it just didn't become a hit." In the meantime, they never pushed it and they released 20 other albums the same month that also needed attention, so a licensor could hardly complain. With pinball machines that's a different story, especially if you know that most marketing efforts are aimed at the newest game. Then again, there could be hurdles along the way preventing a licensed theme from actually making it ito a pinball machine. So the fact that a license has been taken, doesn't have to mean we're going to see such a game. It could just be a business tactic.
As far as Beatles goes, Beatles was JT's dream theme. If Stern had/has the license he may even have been working on it. It's interesting that Steve Ritchie recently named the license as well in his recent Facebook video in which he answered questions. I can't recall him mentioning that theme before.
I heard some rumors about a company going after the Beatles license over a year ago. Apparently, the license would be extremely expensive and there was/is a stipulation that it could only be a limited run of fewer than 2000 units in total (1980 if I recall correctly). As a result, the licensing cost per game would be the highest ever (so far). That doesn't have to be a problem, but it will most likely affect pricing of the game. If any of this, which again are just rumors I heard, is true, it seems to me that doing it as a KaPow type of thing (read: a limited production run at Batman LE or SLE pricing) would be the most likely way to make it economically interesting for a manufacturing party to get involved. Even then you could wonder whether there is demand for that many games. Isn't any Beatles enthusiast that is into pinball more likely to get the Williams game with the Bootles on it? That game reflects the era probably better than a modern game with an LCD, ramps and all other sorts of bells and whistles. When Stern did Elvis, did Elvis fans massively buy that game? I do know of a few rock n roll memorabilia shops that bought a couple of games and they had a hard time selling them. Would that be different for a modern Beatles game? On the other hand, if you think that you can sell almost 2000 Beatles pinball machines at Batman pricing, you're looking at a potential profit of a few million dollars. Worst case scenario you only sell a few hundred games and break even, so business-wise the risk is rather small.
To stay at least a bit authentic in regards to the license, shouldn't a Beatles-themed game be like an EM type of game? In that case, a retheme of Whoa Nellie could work. The 4 rollover lanes at the top could represent the four Beatles and/or their instruments and lighting up the corresponding popbumper. But will that sell at Batman pricing?