Base94 as something added to $base() would be nice, but it would trash output whose decimal equivalent is greater than 2^53, like what happens when you try to translate an entire hash to/from base36.
//echo -a $base($base($sha1(abc),16,36),36,16)
With Base85, it lets you translate groups of 4 binary to groups of 5 text, the way mime translates 3 binary to 4 text. Base85 is different than Mime in that there are 5-character strings which are invalid, because unlike Mime where 64^4 == 256^3, In Base85, 85^5 != 256^4.
