In fact, what happens at Planck's time is extremely poorly understood and there is a ton of different ideas about what happened. The hard part isn't coming up with a new idea. The really hard part is to show that an idea is *wrong*.
Saying, I have this new idea on what happened at t=0 is not very interesting. What people are interested in is to come up with ways that you can show that a certain idea about what happened at t=0 won't work. Also there are about a dozen different proposals for what happened before the BB, and it helps to know what they are so that you don't end up reinventing the wheel.
As you move away from t=0, then things become more and more well understood. If you want to make up wild new models for what happened at Planck's time, you can do that without much trouble. Personally, I find thinking about what happened at t=300,000 years to be more interesting because you *can't* make up anything. At t=300,000, the temperature of the universe is about 3000 kelvin, and I run into things that are 3000 kelvin every day.
Mainstream physics isn't mainstream physics. Part of what makes physics interesting is that it changes surprisingly quickly. There are some basic things that I learned about cosmology in 1991 that are now known to be very wrong.
The big mistake that people make about cosmology is to assume that it's philosophy, when in fact it's quite observational. We know about the coast of Norway because we can map the coast of Norway, and we know about the big bang because we can see and map it.