It'd be great to hear your thoughts/feedback on the tool. Please feel free to reach out to us.
In terms your comment about lock-in I understand your fear and I think a lot of companies will share this. We currently offer PDF/PNG export however due to the interactive nature of our diagrams we're looking into how we can provide an interactive export. An IcePanel file is also an idea we're looking into. We'd love to work with you if you have any specific ideas in this area.
I also have a side business (me and a co-founder), and I'm planning on making the plunge and going full-time on it in the next few months - there too I've used Visio, because it's what I'm used to, and I get a license with our Microsoft Action Pack subscription. Here though, I'd probably prefer to move to a declarative model, like PlantUML (I only recently found out it works with icon sets, so can do things like nice architecture diagrams too).
Aside from that, I'd echo what a couple of others here have said about having a desktop app version, which would work with local, rather than cloud storage - I generally prefer to have full control over my data and how it is managed. I personally wouldn't mind an Electron app (presumably a native app is going to be a lot of work).
I look forward to trying it!