A tool which can combine across different segments would be useful. I do it in Python outside GA.
The python3 bindings are pretty good. I would imagine you could write a data explorer in Electron, and allow it to combine the elements deep in the JSON to derive query statements which applied in the right way, make combined datasets
It's also impossible to combine segments into one GA "dashboard" -So there's a problem there for viewing status of all your trackers, cross-product.
I mean I brute force one python execution state as repeated segment specific fetches to get the segment specific JSON which equates to users, new users, devices, and combine them into one datastructure which can be dumped as .CSV to feed cross-segment charting in excel.
I would make this happen inside python but I work with excel freaks, its kinder not to assume I know the charts they want.
external_combined_datastruct={}
for segment in ['GAXXXXXXX', 'GAYYYYYYYY', 'UAZZZZZZZ'] :
with open_segment_connection_in_GA(segment) as this_seg:
for i in get_segment_data(this_seg):
data = jason.dumps(i.thedata)
for j in data['some']['thing']:
# add to the external combined datastruct
# now.. print the external combined datastruct