According to commits on the Trezor GitHub, work by “zulucrypto” on the Trezor/Stellar integration began public in October/November 2017 and may have been completed in late January of 2018. The pull request has yet to be merged, and once it is, Javascript libraries still need to be created so that web wallets (like the Stellar Account Viewer) can support it.
Development on the Ledger/Stellar integration began in late September 2017 and became available on the Ledger Nano S in late November 2017, so development on the Trezor integration is taking a bit longer.
Once it becomes available, having an alternative to the Ledger Nano S should help with the current out-of-stocks.
