1)  It's important to keep in mind that this problem, while real and growing worse, is mostly on sunny weekends for a few months each year, according to the press release.

2)  Paradise has a 'back door', the Stevens Canyon entrance, which would greatly complicate any quotas, vehicle closures or mass transit plans.  Perhaps the most common daytrip itinerary is WA locals showing 'The Mountain' to visiting family or friends by entering at White River / Sunrise for the morning light, using the Stevens Canyon Road to visit Paradise and exiting via Nisqually Entrance to return to Pugetopolis.

3)  Planning needs to more closely consider the entire park, not just the Nisqually corridor.  Squeezing a full balloon only makes it bulge somewhere else.  There is currently "metered entry" (with up to 90-minute waits) to Sunrise when parking is full, displacing considerable visitation to fragile Tipsoo Lake:

https://twitter.com/MountRainierNPS/status/1293318399980793857

I've noticed expanding trampling at Reflection, Bench, and Snow Lakes at the west end of Stevens Canyon Road since intermittant metered entry was introduced for Paradise a few years ago.  Social media posts suggest that Mowich Lake, the Rainier destination closest to Seattle, is undergoing similar crowding and damage.  The eastern quarter or so of the park is ouside the entrance stations at White River and Stevens Canyon, complicating visitation management.  Park staff at Mowich, White River and Ohana combined is a fraction of the staff available in the Nisqually corridor.

4)  NW Trek, a local wildlife park, has stopped using it's trams and now runs visitor vehicle convoys with podcasts. Even when the pandemic subsides and mass transit becomes safer, banning private vehicles seems unrealistic to me.  Those who can afford in-park lodging, or win a battle with the bots for a campground reservation would probably still have the use of their vehicles and what amounts to head of the line privileges.

5)  My guess is that the total number of parking spaces at Paradise, Longmire and turnouts along the Nisqually corridor is less than three thousand average-sized vehicles.  Adding the twenty miles of pavement with a traveling density of a hundred cars per mile suggests that the maximum capacity of the corridor is about five thousand private vehicles.

6)  The logistics and cost of a Nisqually Corridor mass-transit system seem pretty formidable, even if Stevens Canyon Road became a private vehicle dead-end.  Banning private vehicles would seem to imply locking gates at night and hiring more law enforcement personnel.

A mile-long backup at Nisqually Entrance probably exceeds 250 vehicles, call it 500 visitors per hour to be conservative.   It would be roughly an hour trip to Paradise one-way, with loading, unloading and intermediate stops.  So about fifteen buses (per hour) might be needed for part of the day at the bottom end to haul visitors without separating families.   With sudden weather changes or many people waiting until closing time to leave, there would be asymmetric demand at various locations.  Dozens of buses might be needed to clear large Paradise crowds before midnight.   Even if budgets allowed VC hours to be extended, there really is no building at Paradise large enough to shelter hundreds of visitors waiting for buses delayed by a storm-caused rockfall on Glacier Hill, for example. 

How big a bus barn would be needed to clean, service and store that many buses, and where would it be located? How many tens of millions of dollars should be spent on a seasonal problem?

7)  A parking lot at the start of a mass transit system would need at least one acre for each 200 cars, more for amenities like access lanes, restrooms, and covered loading areas. so 30 acres might be needed for 5000 vehicles.  Toss in another ten acres for a huge septic system and perimeter security patrol road .  The only place inside the park with that much cleared flat ground would be Kautz Creek utility area, currently a dump and helicopter base.  This location would do little or nothing to improve backups three miles below at the entrance, and would squeeze the Westside Road balloon.   A mass-transit station outside the park would harm businesses between that location and the entrance.

8)  I sometimes like to park at obscure turnouts at odd hours and check for animal paths to the river. It's important to me to stay spontaneous and free to change plans with changing conditions.  My park experience would not be improved by being forced onto a canned tour with strangers also wondering why is the bus so dirty and why aren't there more restroom stops.

9)  Reservation systems also have downsides such as additional fees, scalping and suseptibility to technical manipulation, but would be far quicker and cheaper to implement and more flexible to change or expand than using mass transit as a full-time solution for a part-time problem.   I'd like to see something like 25% of weekend and holiday daily capacity remain first come, first served, with three quarters of capacity reservable during the busy season.  Weekdays could be the reverse, with some capacity reservable, but most first-come, first served.  The main expense would be accurate real-time counting of both entries and exits at all entrance stations and improved communications between them.  The greatest difficulty would probably be in finding the political will to set a figure, then say 'enough, we're full for today.'

10)  The quickest improvement of all would be to bar commercial tour buses on weekends and holidays.