Let me rephrase the question then: how long would it take on commodity hardware worth 10,000$ to guess an 8-letter (uppercase, lowercase plus 10 special characters) with known seed words?
Assuming:
Test 2 billion keys per second, which a single high-performance computer might approximately manage.
94 Possible characters:
numbers (10 different ones: 0-9)
letters (52 different ones: A-Z and a-z)
special characters (32 different ones)
Fixed 8 char password (TREZOR pass is not fixed length)
= 94 ^8 possible combinations or 60,956,894,000,000,000,000,000
about 35 days, given our assumptions...
Major caveat: Every time you generate a possible solution you have to test it and check the balances for the given seed + the 8 letter pass phrase, if your doing this on a TREZOR it would take.. well, tens of thousands of years. If you wrote a special program that had the seed pre loaded and just tested the passwords and retrieved the balance for say the first 10 addresses from the master private key it would take hundreds if not thousands of years...
Edit: TL:DR; It really comes down to how many keys you can test (i.e. check for balance) a second, and the answer is not nearly as many as you could generate. It's simply not feasible.