I'm pretty sure that there will be Vaultwiki for IPS4. First IPS4 will need to be stable. It seems there is still a lot of fixing and development going on with IPS4. I am hearing about public beta release coming so that is good.
In general the feedback of IPS4 is not always positive, and it seems that IPS is adjusting the software to the feedback. So its unclear when the beta is to be expected.
Its an important release for IPS, because not only vbulletin is loosing its customers to xenforo, but IPS is also substantially leaking customers to xenforo. While IPS is gaining a significant number of customers from vbulletin, they are loosing around the same amount to XenForo. XF already has gained twice as much customers than IPS and this trend is continuing. See the cookie search: https://tools.digitalpoint.com/cookie-search
If IPS4 disappoints the IPS license holders then that will probably result in a further drop in marketshare for IPS.