45 subclasses would mean every class but Cleric and Wizard get 3, while those two get 7 and 8 respectively. 48 means that Death Domain, Oathbreaker, and one other subclass make it in.
What is that final subclass that breaks the bank? That's about as mysterious to me as the 5 subclasses they'd be adding to round out the Barbarian, Bard, Druid, Ranger, and Sorcerer. I sort of feel like these 6 questionmark subclasses will be something entirely new - remember that they said they wanted the Rules Expansion Gift Set to be as meaningfully expanding the 2024 Core Rules as it is to the 2014 Core Rules.
That would mean that Xanathar's and Tasha's subclasses would be off-limits. I GUESS they could add in outstanding things like the Path of the Battlerager, but I sort of feel like if they haven't revived a subclass from SCAG yet, they don't intend to. Narratively, The Undead replaces The Undying, for example.
I also feel like this could be a chance to reboot some of the early subclass trap options, or else options that step on each other's toes. Death and Grave Domains are a great example - in an ideal game, we'd have one domain that could handle both concepts, given that they're both talking about the Gods of Death.