PECS is so last year! I mean, sure it is a good early intervention, a great way to assess communicative intent and ability, but why are preparation programs and schools STILL focusing on low tech and no tech communication?
Because these interventions are nearly free. Sure, inadequate, inappropriate. But free.
You think PECS is enough? OK. Act of imagination. Go through a whole day without talking. The only thing you can use to get your ideas across is little cards with pictures.
After your experiment, go read about dynamic speech generating devices from PRC, My Tobii and Dynavox.
Kids who are using PECS are AAC users. IDEA protects a child's right to assistive technology, including AAC. And not just cheap, no tech Assistive Technology. Appropriate assistive technology.
PECS is a great temporary early assessment and intervention. But it is really old school.