Thanks for sharing your experience, i will start playing with options.
On first " look" , for business apps important stuff:
login/sign up ( ajax + mysql) - this is fine
push notification - I saw master collection plugin, this is fine too ?
connection with mysql- take data and send - ajax fine too
web services - php + API + ajax - fine too
take geolocation- Construct plugin + php API for GPS- fine too
If i look from freelance angle and what clients need, a lot clients wants some android app to connect with exist website, and problems what you notices about PDF or iframe we can solve with some new plugins -make new plugins and make construct familiar for bussines apps too .