Given the origins of the word digital, if it is restricted to only a single number base, then that must be decimal.
Origin of word digital is a binary signal which controls correspond digit on Nixie tube.
For there is 10 signals, each can have state 0 or 1, so we have:
0000000001 = decimal digit 0
0000000010 = decimal digit 1
0000000100 = decimal digit 2
0000001000 = decimal digit 3
...
1000000000 = decimal digit 9
As you can see these signals controls decimal digits on Nixie tube, each signal = digit, so they called "digital".
This is how it happened historically, so now you cannot name non binary signal as "digital", just because you want. It will leads to confusion.
It just happened that term digital is used for binary signals in electronics and you're needs to accept it as is.
Calling all non-binary discrete systems analog makes the term analog useless,
There is nothing useless, any non-binary discrete signal is analog, just because it is not digital.
For example discrete signal with 16777216 possible levels is analog signal.
The same discrete signal with 4 possible levels is also analog signal.
But discrete signal with 2 possible levels is digital.
Digital signals are used in digital domain. Digital domain uses digital components which work is based on Boolean logic and math.
Analog signals are used in analog domain. Analog domain uses analog circuits, but can be processed in digital domain with conversion.
All pretty clear and easy.