The three tiered model wasn't entirely my idea, it was an Art^2 idea that we hashed out while driving to/from the Bash at the Beach offseason a few years ago.
The idea was that T1 events would be relatively inexpensive (like District or offseason events), and would primarily target colleges and universities to host them. T1 events would also have priority for local teams over far away teams, and T1 events could potentially start the weekend immediately after ship date.
T2 events would basically be the status quo FRC Regional, although on average they would probably be closer to Championship Division size in number of teams.
Teams would have the option at their own discretion whether to compete in T1 events, T2 events, or some combination of both. This is the most fair option going forward because if "walled off" district events are further expanded, it will further restrict the options of other teams. Giving teams the option of how they want to run themselves and how they want to compete is the best option going forward. Mentor/volunteer/student burnout is not an issue, as the decision of where (and how often) to compete at various T1/T2 events is left entirely up to each individual team.
For example, we're good friends with a number of other FRC teams in both New England and around the country. If the "walled off" Michigan district model was expanded elsewhere to a New England or Florida model, we'd almost never have the chance to compete with our friends Exploding Bacon unless we were both at the Championships. But under a T1/T2/T3 system, both of our teams could choose one year to both apply for an open spot at the same T2 event.
The only major aspect of the T1/T2/T3 idea that would need work is to figure out a system to decide which T2 events a team would compete at if they won enough points from T1 events. Perhaps they would have to preliminarily indicate which T2 event they would want to compete at if they won enough T1 points, and that would adjust the number of "open berth" spots at said T2 event.
As for points, getting Chairman's, EI, RAS, or Champion at a T1 event should automatically be enough to get into a T2 event. Getting Finalist and another award should be enough points at getting into a T2 event. Winning Chairman's, EI, or Woodie Flower's at a T1 event would then add you into the running for winning at your corresponding T2 event.
EDIT: There was also a proposal a number of years ago as part of N.E.R.D. (New England Robotics Division) to use the extremely high number of offseason events in New England as "feeder events" for a "offseason Championship", where teams who won at smaller offseason events could get points toward being elegible to compete at a "New England Cup" event in the late fall.