What are Huawei like at updating their camera software down the line?
Fairly poor; they move on quickly to new devices and don't give existing ones much love.
I had a P9 Plus, bought for the camera abilities. Launched on Marshmallow, didn't get an update to Nougat until after Oreo was in full release and available on half a dozen handsets. Presumably because their EMUI skin is so wide-ranging it takes an age to slap it on top of Android.
In that time, the only Huawei apps to update were the tedious we-replaced-something-for-no-reason ones like Calendar and Messages, or the hubs that want you to sign up and do backups to a server you've no idea about. I don't remember a single Camera update, certainly nothing that added features or improved quality.
They've come on in leaps and bounds with hardware features, but their software side is still lacking.