Should I write a rigorous draft before asking for comments?
It's the nature of the work of academia to throw out interesting ideas and have them torn to pieces, and then to pick out what remains and build it into something publishable.

Since you're in the definition phase and have a 10-pager, I'll assume that you've put together a reasonable literature review and/or theoretical underpinning. What remains is to express the intuitive leap sufficiently plausibly that your oversight (supervisors, funding bodies, university review panel, etc) is prepared to back you.

There's no need to have it all worked out - that's the work to be done. You just have to demonstrate that you might be on the right track. Naturally, the closer that 'might be' is to 'are', the better. But if you can demonstrate this much, feel free to ask for comments.