Something that might already be available in open source (in which case apologies, but I haven't found it if it is) that I would potentially find really helpful would be a 'heat map' mapping tool. Basically as a candidate I am already getting (and anticipate this increasing) a number of emails from prospective constituents on a number of different topics. (eg tax dodging, cycling, mental health).
What I would find helpful is a tool whereby I can just pass it a list of postcodes from people who care about a specific issue, and it gives me a heat-map of where in the constituency people who care about that issue tend to live. I think that it would need to be done on distance from each other and not just the number of people in the specific postcode due to low response rates (ie perhaps 20-30 on any particular issue)
Naturally if it is already available then happy to be directed to it - and it's clearly not critical - but potentially interesting if someone is looking for a little programming to play around with.