It is a good question
I don't claim to be an expert on POWER
On the other hand, I got my first computer, TRS-80 Color Computer 3, when I was about 10 and started learning the Motorola 6809. This was really fortunate, because they used the Motorola chipset in my undergraduate studies and I had a huge advantage.
I go wherever a project takes me, from soldering together ham radio equipment to working in quantitative finance.
Most of the free, open source projects I work on are for communications. In this domain, the highest priority is interoperability, it is no use if a user on one platform can't communicate with a user on another platform.
Metcalfe's law tells us that the value of any communications system increases in proportion to the number of users
squared. This emphasizes how important it is for a network like SIP or XMPP to work across architectures.
Rather than designing software exclusively for POWER, my own goals typically involve designing or improving software so that it runs on any current or future platform. This is an important goal.
Some of my recent activities include
starting to investigate bugs in Blenderand
generalizing that to GNU/Linux development