As someone who has often struggled with having pasted some value in as an attribute or parameter, not noticing the presence of internal wiki-dependent stuff (and then being flummoxed about how to get things to appear as intended), I suspect that the == notation would feel very friendly to exactly the people who can be thrown off by the current behavior.
It reads to me like “Please make this attribute/parameter equal what this upcoming thing equals (i.e., how the following string would get parsed if it were encountered in a tiddler).” This feels quite elegant to me!