Also Jeremy Crawford confirmed on twitter that there are no more than 4 of the SCAG subclasses in Xanathar's Guide, and that Forgotten Realms specific subclasses (Like the Purple Dragon Knight and presumably Battlerager and Bladesinger) will not be included.
I did not expect that... I didn't buy SCAG, so if they pick 4 very good subclasses from it, then I will be a bit more motivated to get XGtE. I don't know the mechanics in SCAG, so just going by the character concepts:
Battlerager: doesn't sound different from Berserker, except that it's dwarves only
Arcana domain: considering Mearls' fondness for domains, it's a highly likely pick, but honestly I think it is a bit too trivial
Purple Dragon Knight: too specific
Long Death monk: sounds interesting, but it might be a bit too 'dark' to be picked
Sun Soul monk: too cartoonish
Crown paladin: would be a nice option for LN or 'atheist' paladins
Swashbuckler: well this is the no-brainer really, and it's a good addition for a fairly 'normal' rogue but without criminal flavor
Mastermind: I don't even know what it is...
Storm sorcerer: another easy pick, and personally I think the sorcerer needs as many subclasses as possible
Undying warlock: I love the concept, but I don't think it will be picked
Bladesinger: oh not another gish... and an elf...
If I could pick 4 that I'd want to have in my games, I'd pick
Swashbuckler,
Storm Sorcerer,
Undying Warlock and
Crown Paladin (backup choice:
Long Death Monk).
But I think WotC will choose only the first 2, and then Arcana Cleric and Bladesinger.