Good analysis. Your draw seven deck has been one of my big "I wonder what the london mulligan rule will look like" questions as opposed to the kneejerk "we need to restrict workshop and bazaar"silliness. Narset and Karn are also big questions.
I think its going to take awhile for the format to balance itself out after MH.
This spring is one of the most interesting times in Magic's long hstory.
We have War of the Spark, with so many planeswalker (including a slightly different design approach) cards that ask a lot of questions.
We have the London mulligan rule, which if adopted will alter the way the game is played and shift how we evaluate certain cards.
We have the upcoming Modern Horizons set, which has the potiential to print new cards that carry effects that will easily find a home in Vintage.
It is a fascinating time to be a magic player.
While dredge is the poster child for "what does this do to opening hands" I think the ability to mulligan aggressively for silver bullets is likewise a little brain melty.
Leylines, major hate pieces, power, force of will...the game would change radically if you could actively go fishing for them and potentially still come away with a keepable hand.