Interesting. For myself, I find G accounts useful to retain
(eg 1 app I use, Caltopo, requires G for single signon).
I no longer use G for email, calendar or contacts,
(not for privacy reasons, but because they are unreliable)
but I dont have a problem with directly using the G Play Store
even though it is more annoying than 27 cats on hallucinogens.
The real problem here I think is that while ACalendar does give you a choice
over which accounts/calendars to use, it doesn't give you a choice over which it accesses.