Separately, the point I made in the podcast is that the defining feature of Magic is variance. While lamented in some respects, by being non-deterministic, Magic actually introduces skill aspects that could otherwise not exist. For example, without variance, deck construction would look very differently.
My main point, though, is that different aspects of the game - deck construction rules, floor rules, the sideboard - are all attempts to manage variance in one direction or another.
The 4 card max/60 card min rule fixes variance at a certain rate (that is, create variance - a no minimum deck size could be entirely deterministic).
The best 2/3 match structure and the mulligan are two additional rules (generally floor rules) that try reduce variance in the other direction. That is, matches that are played as best 2 of 3 have less variance that best of one matches. It moves you closer to the statistical norm.
I am of the firm belief that you want to produce a balance of variance into a Goldilocks zone, not too much, but not too little variance either.
My overall fear is that the London rule reduces variance too much. I don't think that decks should have that kind of starting hand consistency. I wouldn't mind it as much if starting deck size were a bit larger, but I think it makes it too easy to find a single card, and also to assemble 2-card combos.
While I have this fear, I also like the fact that the rule should help non-tier one decks the most. The decks that stand to benefit the most are those that are not Xerox, PO or Shops (the three tier 1 decks).
So, for the short term, I think the London rule will be good for the metagame, in the sense of 1) increasing metagame diversity, 2) increasing metagame balance, and 3) increasing win rates for (some) lower tier decks. But the long term effects are harder to gauge, and I am less sanguine in the long run.
Anyway, that is a very brief synopsis of my remarks in the podcast, which were more elaborate and detailed.