First, I want to say I like the honest criticism!
And a +1 to you, with the speedy and thought provoking reply!
It sure made me think!
And this is what I thought about.
You are absolutely right. It is going to be extremely difficult to find something that captures all of what SFML is and does without cluttering the logo. This should be avoided at all costs as logos should be straight forward and even slightly minimalist.
The reason I said the power symbol may appear childish is because it's a bit played out and cliche used in a logo. Just like you said with the ellipse, power symbols are used far too much in logos and banners, but specifically by those from a more immature and irrelevant background than ourselves. It's too vague and overused to have any lasting impact on viewers. I know it will be difficult to come up with something but I suggest we not invest ourselves too much in the "power" logo and iterations of it and perhaps try different shapes all together to see how they fly.
We should establish color schemes and shape themes to help designers focus their efforts on making something that reads closer to what SFML actually is. Laurent can help with this specifically. He hasn't stated clearly what he is looking for and it makes designing a logo like shooting in the dark.
I'm going to personally start experimenting with different colors and shapes to find something that would (if not) capture SFML better, at least be more original.
Thanks again for the reply
I know how hard it can be to take criticism on something one is passionate about. Thanks for being open.