It looks like Slush & Co. don't want to miss out after the Ledger people promised to implement on Monero, but...
Could it be that Trezor people don’t want to lose their customers for Ledger?
In mid June 2017 the CTO of Ledger wallet said on Reddit they would implement Monero, someday. There is no ETA yet and probably will not be any time soon.
Apparently, Slush of Satoshi Labs (the company behind Trezor wallet) is probably not willing to be left behind:
Any time scale of this is as unclear as with the Ledger wallet though: Slush apparently doesn’t have time to work on this so he is looking for someone from the Monero community to do the code. There already is an older implementation of Monero into the Trezor firmware and it needs modifications.