I don't really know DnD's rules about that but being able to cast 2 level 1+ spell with metamagic looks really OP.
I can't imagine how powerfull the sorcerer will be at higher level compared to any other caster.
I think it would be better balanced if you could only use 1 spell + 1 cantrip (or eventually level 1 spell) per turn with this metamagic option.
Casting 2 level 1+ spells has always been available to sorcerers via 5e rules.
A sorcerer can twin spells enabling them to cast 2 Chromatic orbs, cast Haste on two fighters, cast two disintegrates, etc. all in the same round.
A multi-class fighter sorcerer could action surge and cast 4 leveled spells in the same round all according to D&D 5e rules.
Currently in BG3 any caster can cast 2 level 1+ spells in the same round by consuming a Potion of Speed.
Also any caster can cast 2 level 1+ spells if one has a casting time of a bonus action and the other has a casting time of an action.
