I think there are a lot of really useful features in 2.7 (and subsequent versions up to the current 2.8.0).
It looks like the wallet format was upgraded in 2.7.0, and that this format does not support multiple accounts within a single wallet (including if you are using Trezor or another hardware wallet).
My question is, was there a technical reason why this is not possible in the new format? I personally think that the ability to use multiple accounts was a great feature for a number of reasons (including privacy), and would like to see it available again in future versions of electrum, if possible.
I acknowledge that it is possible to simple have multiple electrum wallets, and to even have multiple electrum windows open at the same time.
From what I can tell, this is due to the switch from bip32 to bip39. The multiple "accounts" as a concept is part of bip32 and isn't part of bip39 ( which added the mnemonic code )