There are side effects using script amp in standard html5 pages?
My idea is to use amp-iframe to show some related content, also in web pages and not only in amp pages.<
I have tried some month ago.
My idea was to use the https://cdn.ampproject.org/v0.js
to load images async for performance.
Same to use the flying carpet and the Carousel on my regular site. The result was the internal validator brings to much errors, the script breaks, you need the Boilerplate and so on.
So the answer is you can't use the AMP script on a 'normal' HTML site. Or you take the script and modify it for you. But you will lost the on going support of all changes.
I haven't seen side effects yet of a nonamp/amp hybrid page. I'm currently using https://cdn.ampproject.org/v0.js for img control (ex: lazy load) on a non amp page.
I'll guess this is not the type of bad coding that Google will result in a rank penalty.
My nonamp page has:
Images didn't show up on Blu windows 8 phone. Suspect amp script at fault. Images do show up on Android smartphone.