I think, it doesn't matter why to install OL8. Compare to Microsoft/Redhat: if they offer a new release centralized Patchmanagement is available.
There is no alternative to centralized patch management for OL 8 other than Spacewalk? I don't think your assessment comparing with Microsoft or Red Hat is fair, because neither will offer you a perspective continuing with Spacewalk. The author of Spacewalk is Red Hat, not Oracle, hence Oracle cannot be held responsible for any strategic decisions made by Red Hat.
However, my response was not about criticizing your motives for upgrading, but to suggest a more pragmatic approach of the situation. You will obviously have to look for an alternative to Spacewalk at some time now or in the future. One of the key reasons for using Enterprise Linux is long term support. So, unless you are forced into upgrading right now, for whatever reason, you may still have enough time to plan ahead and evaluate your options. Are you using the Oracle Linux kernel? That should also buy you some more time to postpone upgrading until you are ready, at least from the perspective of the kernel.
today I read that spacewalk project has been discontinued. Does it mean that no more evaluating on spacewalk 2.10 on oracle side?
Does it mean that no more evaluating on spacewalk 2.10 on oracle side?
No, it doesn't. We're actually adding features to our Spacewalk 2.10 release to make it more compatible with Oracle Linux 8.