I think that you should fulfill your obligation at your current company and do the demo. The company you are interviewing with will understand your situation if they are professional enough. Go out strong and do the right thing, while maintaining your network and reputation. My two cents.
I think adding a 'Prioritize' feature would be very useful and beneficial. That way you can 'rank' your tasks and sort through them on a number based system.
I think there is a common trend where start ups focus on product and gaining users while then thinking business model second. What are your thoughts on 'Freemium' as a business model? http://bit.ly/eMxey0
This book http://www.businessmodelgeneration.com/ is an invaluable resource for entrepreneurs. I am constantly working on my business model canvas because it provides great insight and a clear overview of your start up.