Will the Epinio UI be merged within the next version of the Rancher UI?

Sorry I have no answer to this. It doesn't depend only on Epinio's backlog and priorities so it's hard to estimate delivery. Maybe @high-morning-12231 has some rough estimation.

The Epinio UI won't be in Rancher 2.6.5 (just released) or 2.6.6. We have a prototype of Epinio UI within the dashboard, however at the moment we're concentrating on the independent UI served by each Epinio instance.

The reasoning is that there is some functionality missing in Rancher that makes integration awkward from a UX perspective. I will make the case for prioritization of these features soon