For now SIP can be disabled (on mac, not of course on iOS that is completely closed) but I wonder for how much. It's clear that the desire of Apple is to make macOS a closed system like iOS, installing third party software outside the AppStore is more and more difficult, with Gatekeeper that asks you to enter the system settings and warn about "potential insecure stuff" each time you want to run an application downloaded from the internet not signed by Apple (yes I know that if you disable SIP you can get rid of Gatekeeper as well).

I think that piece by piece Apple wants to go into direction of making macOS just a desktop version of iOS, that is closed and impossible to modify. They will use of course security as an excuse, the practical thing is that with iOS they succeeded because they went to the market with an OS that was already closed, but making users accept that in new version downloading a software from the internet and installing it it's no longer possible takes time. But they are getting there soon to me.