IDE and FMP are mutually exclusive concepts. FileMaker is not a tool designed for developers and never will be and as such an environment such as you describe will never come forth from FileMaker but it's a nice suggestion
I wonder if we have come to believe that only one piece of software is all that is needed. Of course it must create edit and handle bitmap graphics, vector graphics, formatted text, data manipulation, form creation, OCR, and work across all platforms and OS, have the speed of development of open source but the stability and security of a major enterprise and delivered in the front end of my choice.
I LOVE the environment that FM gives me to work in, and while I am active in making suggestions for improvement and extend it in many ways, I am personally not that supportive of changing the core concept.