I don't think we need to worry until all the Macs have such chips inside. The iMac Pro (and probably the future Macs that include the chip) does require the chip for "Secure Boot" (but the feature apparently can be disabled for now), but for other current and older Macs that can support High Sierra and which do not have such a chip Apple has to ensure that High Sierra can boot on them without any kind of "Secure Boot".
But yes, I expect future Macs, not just the iMac Pro, to include such a chip to support "Secure Boot" and other functions.
PCs from major OEM manufacturers already support their own version of "Secure Boot" in their firmware in order for Windows 10 to boot on them, and I have heard that on some of those PCs you may not be able to turn that feature off, which means you can't boot other operating systems which do not support the version of "Secure Boot" on them, including older versions of Windows and maybe MacOS.
The motherboards we bought for use in running Windows and MacOS mostly allow for the switching off of "Secure Boot" (that "Other OS" setting), which is why we can install MacOS and/or older versions of Windows such as Windows 7 on them.
I think we should worry more about motherboard manufacturers removing the option of disabling Secure Boot in future releases (since new PC hardware is supposed to support Windows 10 only so they do not expect users to be able to install older Windows versions which require disabling of Secure Boot), as such a move will probably mean we can no longer install operating systems other than Windows 10 (and Linux versions that can support Secure Boot) on the new hardware, including MacOS.
