I've been using illumos on and off since it was called "OpenSolaris" and illumos is rapidly becoming less relevant just due to the tiny ecosystem. dtrace and mdb are both great tools, but it's getting to the point where ZFS on Linux (which possibly can't even be shipped as a binary without violating the Linux EULA) is seeing more usage than all other downstream consumers (and ZFS/FreeBSD was probably a wider usage than Illumos for a long while now).

Ultimately being a libre *nix that is better in a few ways than Linux seems to be a long-term losing proposition, as Linux will eventually check all the boxes you (even if it's not quite as nice) thus steadily shrinking your niche.