With currently only 3400 paying users it's only 80K pr. year of revenues (and the profits are probably much lower). It's still far from a good business and this kind of money does not have any kind of guarantees.
That's at least $200,000/yr with high margins.
The amount of annual income from this product will now end with "million".
still should easily net him a nice recurring six figure salary.
He reaches $1 million at just over 40k paid users.
Factor in the userbase he's already been building for 4 years, the hundreds of thousands of Google Readers currently leaving, the millions that will need to find a replacement before July, and the last-minute movers on July 1st.
I don't think server costs and a couple of employees will put him below a 7 figure income.