My personal opinion: for any project in which you’re the sole resource (engineer, product manager, subject matter expert, UX, QA, etc. etc.), if you want to be remotely successful, you must pick something that you want and will personally use.
If not, you simply won’t have the insight needed to design and build a useful product. Also without meaningful use, you’ll be blind to the product’s shortcomings.
To have the motivation needed to power through the tough times by yourself, e.g. when you’re really tired of working on it or have other competing obligations it should really be something that you’re personally passionate about.
If you build a product based on your assumptions of what other people want without the resources to test these assumptions, you run the risk of making something that isn’t useful to anyone.