Of course the "optimal one" would be base "e" but nobody is going to be able to do anything remotely reasonable with it... (pg. 491 of that manuscript).
Well, you could... if you want to give up discrete integer representation...
Anyway, if ternary is actually optional in practice depends as much on how efficient the ternary logic can be implemented on a silicon process. If you increase integer storage efficiency by 10%, but circuit density decreases, maybe you're not getting enough value.
Okay but what's the significance of (non-unity) powers of e? e is the optimum of a specific function[1], and you lose the benefits for higher values.
It's true that you can conveniently represent the numbers by using integer powers of the base (like representing binary with hexadecimal), but the whole reason e is a "good" base in the first place is because you're (partially) minimizing the number of distinct symbols needed to represent a number, and you lose that once you go to a higher base.
Plus, using a slightly-off integer like 7 breaks the integer-power-mapping anyway.
