Suggesting that "no one will queue for MSQ" is simply inaccurate (as in, you have no way of proving this statement). At any point after this change, the non-new players queuing will be greater than 0 (it is far more likely than not that this statement holds).
It will almost unquestionably be less. This isn't hard to discern, just from looking over the backlash that has already been made before the patch is even live.

In accordance with the above, putting myself in the shoes of a new player, I would rather wait a longer time for these dungeons, if a shorter time means getting yelled at to skip skip skip. S-E, apparently, agrees.
They're still going to be yelled at to spam through the CS like everyone else and will get vote kicked when they don't.

Refitting the Leveling Roulette to accommodate for 8 player dungeons is very, very simple. It is not this enormous undertaking that has been suggested.
This is the only one you're right about, because guildhest roulette has a 8 man hest too.