There's a lot to unpack here, so I'll try to cover various points.
Big Sky has outgrown its tram. They got to the point where the option was to have 2 hour lines every weekend, or make it an upcharge, so they made it an upcharge. It was built in 1995, when Big Sky had a fraction of the skier visits they do now. I don't know the exact number, but I know it's over 500k now, which was considered a far-fetched dream back then. Even if they didn't have capacity issues, that tram is still on borrowed time. The bottom terminal is situated on a rock glacier. That means there's several feet of rock on top of ice, and it moves like a glacier. The terminal has actually slid several feet downhill and started to lean. While the system is designed to accommodate some ground movement, and the lift is perfectly safe now, there will be a point where it gets to be too much.
Boyne has not yet revealed the capacity of the new tram, but it will be more than the current one, both in terms of the number of people in the cabins, and total throughput. I don't see it causing too much of a problem with the terrain. Nearby Jackson Hole has a much bigger tram, and that doesn't seem to cause the terrain to get skied off. The change of the bottom terminal, and extension of the lift is necessitated by ground movement, but it will have the added benefit of a direct transfer from the gondola. This means that combined with the gondola, there's direct access from base to summit, so anyone, whether they ski down or not, can at least go to the summit. I wouldn't be surprised if there is more foot traffic than skier traffic. It also allows the tram to operate year-round.
As for the gondola, it accomplishes several goals. While the upgrade of Swift Current from a quad to a bubble 6 helps, the fact is, they really need 2 lifts out of the main base, going in that direction. The only lift from the looker's right side of the base is the Explorer Double. It's a Heron-Poma from 1973, the resort's last remaining original lift. Just like the tram, the resort has outgrown this lift, and it is inadequate as the only beginner lift on that side of the resort. The gondola replaces Explorer and is extended to where the old Gondola One ended, creating a second route from the base to the upper mountain. From the top, you'll be able to access any lift that you can get to from Swift Current, though Swift Current is still better positioned for lapping the intermediate runs that return to the base. However, the gondola does provide direct access to the easiest trails that return to the base, making for excellent teaching terrain. Gondolas work well as beginner lifts, though few resorts can afford them for this application. One instructor can take an entire group lesson in one cabin, and not worry about if kids can't get the safety bar down on a chair. It will also provide a way for foot traffic to access the tram in all seasons. Capacity is said to be similar to that of Ramcharger 8, and the combined capacity between Ramcharger 8, Swift Current 6, and the gondola will be around 10k an hour.
The lodge facilities that are located at the gondola stations also solve yet another problem. Big Sky has outgrown its base facilities, and the gondola relocates the ski school to a new mid-mountain facility. Big Sky also lacks an upper mountain lodge on that side of the resort. Only Andesite has it with Everett's 8800 at the top of Ramcharger 8. The lodge at the top of the gondola will fulfill that need, and you'll be able to go between lapping Powder Seeker, the tram, Shedhorn, and Dakota without returning to the base.
I also want to address the naysayer comments in this thread. I find it just totally whacked out to be complaining about improvements Boyne is making at Big Sky. Locals are presumably there a lot, and are aware of the resort's shortcomings, which Boyne is making efforts to address. Clearly, they are trying to upgrade Big Sky so that the resort can accommodate a million plus skier visits in the future, and in doing so, they're providing an experience that's unlike any other resort in North America. That's better than what Vail has done where they let their resort's get overrun and didn't make improvements to accommodate more skiers. Yes, there might be more people on some trails, and yes things might get tracked out a bit sooner, but Big Sky can easily handle many more skier visits than they do now, and more comfortably than Vail Resorts is. Yes, I know there's often a desire among locals for there to be fewer skiers. Not only does this mentality reek of selfishness and entitlement, but I don't think you'll like the result if they actually tried to do that. Either they need to dramatically raise prices, implement reservation systems, or both. You'll end up paying more, not being able to ski on all the days you want to, or both. You need to consider all the benefits and drawbacks of what you're supporting.