Following the recent events, wait until multinational corporation x comes, repackages your software as a managed solution, hosted on their infrastructure and resells it through their channels.
See my comment as a snarky reply to the recent HN threads about the aws/elastic debate, not as a serious contribution.
Although on a more serious note, I can clearly remember self appointed knights of FOSS claiming on those threads that AGPL is bad because it harms adoption.
I see it more as a form of protection against corporate exploitation, apparently OP does too.
Online invoicing is hardly an area unexplored by large corporate SaaS companies. The world is a big place and it seems he's found a niche he can make money in.