A reserved fan ebug is a no go for reasons you stated and others.
An extra roster spot might work, but that's potentially someone playing not very much hockey. OTOH, we already have that scenario since it's a 23 person roster.
The thing is, this latest ebug appearance was kind of an important game. Goalies seem to get hurt more often now (someone just got hurt tonight), and as good as these stories are, you probably don't want to see an ebug when it matters.
Maybe just add the roster spot after the trade deadline or something
And I do think keeping talent playing rather than coaching is one of the primary reasons they don't change the rule. With my rule change, if you're a 24 year old ECHL goalie how much money would it take to accept an EBUG "trainer" job? How would the cap deal with that could also be an issue.
I doubt traveling expense is the limiter, how many years of that would it take to reach even the NHL minimum salary?
Teams would try to game the system if they were given more choice, and it'd lead to more decent goalies riding the bench rather than playing in smaller leagues.