The first post of this thread is citing "roof complexity" as the unforeseen reason. The link they send people to says:
You will be notified if we assign a new level of complexity to your roof and your purchase price will be updated to reflect this after your system design is complete.
Inferring from the link they pointed people to, further review of the homeowner's unique project (the complexities of the roof heights, planes, obstructions, pitch, etc) have now factored into their latest assessment of complexity and costs.
I think it would be unprecedented (at least, as far as I'm aware in residential construction) if an arbitrator compelled Tesla to begin/complete their solar roof at the previously committed price. It's more likely an arbitrator will award damages for people having relied on the expectation of having a Tesla Solar Shingle Roof installed.
But I'm still hoping folks like
@Bill_woolf chime in with feedback that says a lawyer is willing to push their case to get their Solar Roof at the original contract.