Addendum:

>> Will MorphOS also be Spectre and Meltdown compatible? ;-)

> It's already Spectre-compatible on PowerPC / Power Architecture ;-)

Regarding Meltdown:

When IBM revealed some weeks ago that POWER7(+), POWER8(+) and POWER9 (pre-current steppings) were vulnerable to Meltdown, they failed to give any information on pre-POWER7 processors. 3 days ago this follow-up was published:

"IBM will not be releasing patches for POWER4, POWER5, POWER6 systems and recommends migrating to a more current generation of POWER technology. [...] on February 6, we will introduce an offer for pre-POWER7 clients to upgrade their security profile and protect against Spectre and Meltdown through the purchase of POWER8 or POWER9 systems and available migration services, security support, and financing offers."
https://www.ibm.com/blogs/psirt/potential-impact-processors-power-family/

Does this mean POWER4 might be vulnerable to Meltdown? And if so, this would mean the POWER4-derived G5/PPC970 is most likely vulnerable as well, right?