Why don't we see anything in Download section, both Stable and Unstable links?
If there supposed to be empty space, maybe it's better to remove the Download section from the site?
I think that is because Illumos currently does not yet have posted releases .
Take a look at the Wiki, at the "how to build Illumos". (That is also the explanation how to update from OpenSolaris snv_134 to 145 and then to Illumos Boot Environment, after building Illumos.)