Recently i've heard about the Accelerated Mobile Pages project, and read some info about it.
I wonder how to implement it for existing website that is built upon Ionic and Angular?
Basically there is no nearly possible solution to do that. If you check the doc here.
Keep all third-party JavaScript out of the critical path
Third-party JS likes to use synchronous JS loading. They also like to document.write more sync scripts. For example, If you five ads, and each does three sync loads, with a 1 second latency connection, you’re in 18 seconds of load time just for JS loading.
AMP pages allow third-party JavaScript but only in sandboxed iframes. By banning them into iframes, they can’t block execution of the main page. Even if they trigger multiple style re-calculations, their tiny iframes have very little DOM.
Style-recalculations and layouts are typical to DOM size, so the iframe recalculations are very fast compared to a recalculating styles and layout for the page.
来源：https://stackoverflow.com/questions/35582471/how-can-i-implement-amp-in-angular-ionic-website