Hope you don't mind if I offer some elaboration on what works so well:
You get blade cantrips that scale to player level
You can bonus action quicken cast GFB or booming blade for a second attack.
You can hold your main action, quicken cast GFB, and then on someone else's turn you can use your readied action to cast green flame blade again and still proc sneak attack.
It sounds more exploitative than it is because you'll have lost a lot of sneak attack dice to get those sorc levels.
Eventually you can use haste to ready your main action, try a normal sneak attack, and then bonus action quicken a gfb.
Supposing you're at rogue 6 -> sorc 5, you're looking at
Bonus action: 1d8 (rapier) +4(mod)+2d8(GFB)+3d6
Haste attack: 1d8+4+3d6
Readied action: 1d8+8+2d8+3d6
= 74 DPR
Pretty strong, but dependent on concentration and a limited supply of sorcery points.