Nope. Never seemed appealing to me, as I have easily installed Nagios with the graphing plugins and other added features in the past by hand - for a few companies at least.

One of the biggest wins of Icinga2 for Nagios shops is the fact that it can be sort of retrofitted to work with your existing Nagios hosts using NRPE.

Of course, NRPE is highly insecure and this is not recommended, blah blah, but it works, and I'm sure there are more than just a few people still using and older version of NRPE in production.

Oh, hmm I think that might be a new limitation then. (Which only makes sense since they gotta make money somehow...)

25 hosts: free. 26 hosts: high costs.

Yeah, they could make that more appealing :)

If you are worried about spending money when expanding to 26 hosts, you aren't their market anyway. If you're worried about spending a few grand on monitoring for around ~100 hosts or more, then you have a very strange business model.

The problem is 26 bare metal servers is very different from 26 VPSes.