Any pitch that starts with "this may not be possible" (even if that is inferred) is going to quickly get turned off by anybody who listens to pitches all the time.
This is why engineers generally don't make good sales people: the desire to tell the whole truth is usually too strong. The world of software is an incredibly dynamic space, so sales and marketing can use a little of that to their advantage. :)
It's impossible to know with 100% accuracy if a great idea will be possible or not. This is one of the reasons why I like the Lean Startup stuff so much, where you can be honest (with yourself, at least) about doing just enough to prove if something is possible/marketable/whatever before investing years and millions into it.
This is why engineers generally don't make good sales people: the desire to tell the whole truth is usually too strong. The world of software is an incredibly dynamic space, so sales and marketing can use a little of that to their advantage. :)