Yes, of course, I would be. There is actually a larger community of blind navi junkies in Poland so you would receive a bunch of valuable feedback.
The argument with holding phone in your hand vs. in your pocket is an important one. We use navigation for other things than sighted people sometimes. Often I wished I had a way to carry my cane in one hand, a bag of shopping in the other and still be able to handle my navigation as I find my way from that shop back to home, to the hotel etc. I don't know much about what is possible in web-apps and what is not so I can only keep my fingers crossed.
One thing I found always missing, especially when I was beginning my adventure with accessible navigation, was a system of meaningful messages telling me how to interpret the data I receive, for instance, based on my bearing direction I wished I could hear things like "You're going wrong, turn around" or "You're back on the right path, carry on". This could be a special beginner's mode thing and could be disabled by those who feel advanced enough.
Also, it would be great if using the available POI from OSM, the next turn announcement could carry more contextual information E.G. in order to reach your turn, you will have to cross the street to the other side on the way or that there are stairs to be taken, fixed obstacles on the way that are noted in the database etc. just so that the user knows what to expect on the way. It could also determine which side of the sidewalk to take based on the heading direction and available map data. This could be useful again for people just learning how orientation works but somehow I feel I would use that too.
How doable are voice commands for hands-free operation? Of course at a later stage, when you're comfortable with the basics.
Have you looked into Microsoft's mapping API's. Those could be less expensive than Google.
Also, spatial sound seems to be a thing with navigation now. Have you seen GRMapa for instance?
A lot of users seem to be happy with how it lets you imagine the correlations between streets.
I know this is a lot but I am really curious how far this can go.
Looking forward to releases.