As I get closer to upgrading the live forum, I'll have a test forum setup running the new software. At some point I'll invite some people into that forum to help test it out, report any problems and make suggestions on how to improve it. I have a fair bit of work ahead of me before I get to that point, though. My plan is to devote focused attention to this task in about a month. I'm also waiting for Invision to release version 4.3 of the software, which includes direct support for ElasticSearch.
Invision completely rewrote the software from scratch going from 3.x (what we're running now) to 4.x. No existing third-party modifications (hooks, apps, etc) work, no existing third-party skins work, so all of these have had to be reprogrammed or recreated for 4.x. I have several custom modifications in the code here, such as the ability to give people permission to edit specific posts, or to set entire forums as editable (marketplace and programming forums, for instance). All of these will need to be recreated, which means I need to become familiar with the new software "under the hood" so I can re-implement these features. And I need to find suitable replacements for third-party software I've been using. And I plan on adding some new features that I've spoken about before, such as the "Downloads" module..
Should be interesting when the updated forum goes live, to say the least!