Based on a "plan to release the ISO sooner rather than later" comment by a team member in another thread, I'm expecting that the new ISO's will be released in late May. That seems a reasonable time frame.
I expect that Solus will be listed as "Dormant" until the new ISO is released.
As far as I know, there is no reason why existing Solus users will need to install the new ISO, so long as all updates have been applied as released.
Because I did some dicing on my existing build during the interim, and no longer trust my existing build, however, I intend to do a clean install from the new ISO, and my Solus laptop will remain fallow until then.