I couldn't care less about Powerplay, as it's fundamentally flawed (and the other suggestions in the linked thread don't change that), but I agree with Vardaugas: this sets a troubling precedence. There already are people clamouring for making the BGS open only as loud as they have been for making PP open only, and now FDev has set the first step on that slippery slope.
First they came for Solo Powerplay - but I did not speak out, as I don't do Powerplay.
Then they came for Solo BGS - but I did not speak out, as I don't do BGS.
Then they came for Solo CGs - but I did not speak out, as I don't do CGs.
When they came for me - there was no one left to speak for me.
Which means:
If you play only in Solo\PG and never play in Open,
PROTEST against Open-only Powerplay\BGS\CG\whatever. Even if you don't do the said activity, and don't plan to do it. Otherwise, they may come for you next.