This may sound crazy but my sight reading improved a lot after I took an ear training class that required me to work in arbitrary clefs. I always knew treble and bass from playing piano, and had really memorized the note positions in each.
When I was suddenly forced to work in tenor, alto, soprano, baritone clefs, I could no longer rely on memorization of note positions. I had to pivot to “reading intervals”. A fifth looks the same in any clef, so if you know the current note, and the next note is a fifth above, you know the next note too, clef be damned.
Really? I don't think all fifths look the same even if they're all in the same clef. If you're working in C major, B to F looks like it's a fifth, but it's a tritone. Everything around this becomes a little weird; A# to E# looks like a fifth and is one, but A# to F is a fifth and doesn't look like one.
Random clefs seem like they would make that problem worse.
When I was suddenly forced to work in tenor, alto, soprano, baritone clefs, I could no longer rely on memorization of note positions. I had to pivot to “reading intervals”. A fifth looks the same in any clef, so if you know the current note, and the next note is a fifth above, you know the next note too, clef be damned.