I think what a lot of people are concerned about is the rolling-release
aspect of this. There will be no definitive versioning of CentOS in the future - all you will be able to say is "fully updated" and it won't be possible to slot a CentOS system in to exactly match a RHEL version. Will third party RPMs built against RHEL 8.x be installable on a CentOS 8 Stream system? The answer is surely "it depends", but there are a lot of hardware vendors that target drivers to RHEL releases, which may well make CentOS non-viable for hardware that doesn't have drivers built in to the kernel.
Generally if they follow the ABI guidelines I would expect it to work. Those are here: https://access.redhat.com/articles/rhel8-abi-compatibility
For loadable kernel modules there's a kernel ABI.
Yes, and many things work well. My most recent issue was that kit supplied by HPE (sorry, it's pain is stuck in my mind) had a RAID controller that needs a driver disk during install - doing the install time drivers is not a problem, the problem is that they don't support CentOS, hence I had to use a RHEL driver and out of the 5 available for RHEL7/8, only one of them worked with a CentOS release. HPE support don't want to know because they don't support CentOS.
I know this comes under the heading of "Corporate RedHat Policy", but is RedHat going to do the right thing by CentOS 8 Stream to the level of lobbying other behemoth corporations such as HPE or Dell to support it?
P.