I would way rather standardize the sounds like how Japanese does it (mostly) than have accents. I've never liked accents. I'm considering learning Ido over Esperanto because of this very issue.
This has been tried.
https://luminusdadon.wordpress.com/2006/05/04/how-english-be...
For example, "Co" would be pronounced like "Tso", whereas "Ĉo" would be pronounced like "Cho".
Pronunciation is completely standardised, with stress (almost?) always placed on the penultimate syllable.