I'd love to connect to compare notes. I'm well on way to $50k/month, but I have a feeling I can attain that revenue without a few of your bullet points.
* B2B niche - agreed, this is essential
* Viral component - I wish I could make label printing viral... but I feel like I'm dealing in the "colonoscopy of software" with my app
* Only subscription - I agree this maximizes revenue, but I find subscriptions user-hostile, so I also sell a one-time license
* Subscription expiration - obviously essential
* Generous trial - agreed, essential