Android oreo is been tested on Chinese phones atm.
Bootloader locking is another case. You will get official updates with bootloader locked but no if you have customized firmware Why they do that is because Huawei have their only firmware and they are aware that many devices broke down by users trying to put custom firmware. After updating from custom firmware to official many times the device is missing very vital things. Also. As long you have a bootloader code i dont think it will affect you in the future. The main problem will be with new devices sold after a certain day
On one side users don't dare to research before they brick devices.
On the other side developers and communities behind (certain) custom ROMs do not dare to put clear info how to go back from their custom ROM to stock.
Generally it's easy, go first back to stock (use HWOTA, no-check Recovery or even HuRupdater) to the build one was before installing custom ROM (some users don't even remember which stock they previously had) and after that upgrade, rebrand, whatever.
But it's 'too complicated' for some, they think they can uupdate directly from custom to the latest stock, sometimes even forcing diff cust.
Some also think it will help if they first relock Bootloader - induced Factory reset fails but TWRP is gone and FRP relocked and there is no more system - then they start to cry...
All these things are written elswhere but many don't bother to read before they run themselves to the problems