OK, I'm not sure if anyone else is commenting on the significance of Rum, but this is the first time in 900 chapters of Conan that we meet a character with a higher rank than Gin, whom I will remind we met in Chapter 1. Vermouth's about the same as Gin and obviously "the boss" doesn't count as there's no indication he'll appear anytime soon, but it's clear that we're on Rum's arc and Conan's next showdown is with Rum.
Point is this: we can finally rationally speculate on when Conan's going to end. I think Rum's appearance proves that we're nearing the beginning of the end, since when Guy #2 is after Conan, you know we're in the big leagues now. The only guy scarier than Rum is the boss.
Let's first look at Conan's plot structure... I think Conan really has had 3 major periods.
Act 1 (Chapters 1-175): Prologue
This goes from the very beginning to the introduction of Sherry. There's basically NO real "plot" in this period to this beyond some (albeit key) character development. The BO characters (Akemi, Tequila) appear in like one episode and die as soon as they are introduced. Conan also doesn't have any plan of fighting the BO beyond waiting at the Mouri Detective Agency.
Act 2 (Chapters 176-434): Sherry vs Vermouth
In my opinion, the golden age of Conan. Haibara's appearance really shook up the series by actually giving the plot some form of direction and the arc goes deep into both Haibara and Vermouth and their past. I think this is kinda like the Soul Society arc, as Conan was at the height of its popularity and when people think of Conan, they think of the Matsuda case, Desperate Revival, full moon confrontation, ie this era.
Interlude (Chapters 435-500): Seven Children
The "reset" button. I think this is the major turning point for Conan as Gosho realized that he's divulging too much information for the series to stretch and basically stops a lot of the character development. Yes, there are exceptions, but just look at the casualties, the most obvious of which are Detective Boys. Does anyone remember Ayumi's crush on Conan? Mitsuhiko's on both Ai AND Ayumi? Overnight, they just gave up, went home and turned into cardboard boxes. Also wtf happened to Ai and Vermouth? Yes, they appear, but can we give ONE interesting new thing that we learn about either past chapter 435, neither mind the old lingering questions?
Act 3 (Chapters 501-898): The Infiltration of Kir
The series rises from the ashes by focusing on the new character Kir. This act's a bit harder to pinpoint as it's really two separate arcs: Kir/Eisuke and Akai/Bourbon with the infamous clash in the middle, but the overall theme of successfully infiltrating Kir into the BO is the main focus here. In a way, the plot almost goes backwards. Conan goes from dueling directly with Gin and Vermouth (hell, almost capturing her) and getting the freaking boss's phone number to... dealing with their lackeys (eg Chianti, Korn, Bourbon, etc.) aka guys that VODKA can possibly boss around.
So this brings us to Rum, which is the first time that says that to me that we're nearing the beginning of the end of Conan. So... does this mean that Conan's going to end soon? Well, maybe, but probably not. There will be at least two more acts:
Act 4 (Chapters 899 -

Act 5 (Chapters


So what does this mean? Kir's arc lasted almost 10 years (Bourbon's itself almost 7), so I can't see think Rum's arc lasting under 3 years and the boss's arc under 5 and it's quite likely that he will insert another arc in there somewhere (I think Gin having an arc is a good guess since we know nothing about that guy's history). Gosho Aoyama is currently 51, so it really looks like he's got it planned out. At the earliest, I see Conan will last another 9 years until his legal retirement in Japan. But since Gosho's drawing less and less as he gets older, I really can see him going for another..... 20 years even.
TL;DR For the first time in decades, we can see a glimpse of Gosho's future plans with Conan. I think Conan will last until 2025 at the earliest, but more reasonably around 2030 or beyond. What do you guys think?