Congratulations on releasing the RC version for both 6.0 and 5.4!

As requested I'm testing these versions and I am running into some uncertainties while updating my extensions.
What is the status of functions that are 'deprecated and will be removed in 6.0' that are still in the RC version?

is it safe to assume that these will stay in and that the notice will change to 'removed in 7.0'?

As an example:
I am using install scripts that extend InstallerScript
this gives the following notice: 'Legacy installer files are deprecated and will be removed in 6.0. Use a service provider instead.'

So I need to refactor my scripts into Service Providers that implement InstallerScriptInterface. Because I need the functions in the InstallerScript (like: checking minimum versions, etc.) I use the InstallerScriptTrait.php

This works great, but it makes this script impossible to run on Joomla 5.4 as that version is missing the InstallerScriptTrait.php

This makes it with the RC versions unclear as to what to do: refactor and not able to run on J5.4 or stick to what it is now with the risk of not working due to removed code in both 5.4 and 6.0

can somebody give some insight as to what the status is, to avoid making assumptions and running into issues later on.