I do understand half of it, like said before the dev's always hold off and select the best way to go forward with 1 of the possibilities, keeping the other exploits for later jailbreaks.
With corona they elected to put the effort in pod2g exploit instead of MuscleNerd's earlier exploit, both used developer tools which they needed to evade to release to the public.
All the dev's are now twittering about i0nic's untethered exploit, in one of his last tweets he says his is the only untethered one. So it's not only the developer tools, MN and Chpwn only have a tethered version.
What ionic does or doesn't do isn't always a matter of instant public record.
My guess is they are now testing the jailbreak to look for bugs, they always do, is done by several people and it takes a bit of time, after that is done it will be turned over to one of the dev teams for a public release container.
He won't sit on it, he's just playing with everyone, that's his style.