When David Page announced pgAdmin 4, I was really excited to try it out. I was impressed I could compile it so easily on windows. I had a few bumps, but not too bad.
One of the reasons I'm excited about it is that it's built on Python and a web framework, and there is a large Python and web developer following in the GIS community, so I suspect someone will step up to the plate to add a mapviewer plugin to this so I can have a seamless PostGIS experience.
The interface is also very slick and pretty and I love the sorting and paging capability now in the query window. Check this sampling from our workshop database.
Please consider including a JSON formatter / validator such as https://jsonformatter.curiousconcept.com/.
This would make the JSON(B) workflow much simpler by (a) using pgAdminX to troubleshoot formatting errors on load and (b) reviewing JSON (B) output with the same tools we review other data types and (C) eliminated the tedious step of SELECT JSONB_PRETTY() + copy + paste into text editor.