Great work!
I'm having the idea to try to reball the eMMC as well, didn't get the courage yet

Did you have trouble while detaching the chip from the stencil after reflowing the solder paste? And what were the temperatures used in all the steps?
Thanks!
well go ahead no risk no fun just take ur time and dont use to much heat Xd
i starte with preheating the board for 1 min with 100°C then 1 min 200°C after that i went to 280°C waitet a fes and checked if it moved didnt so i bumped it up to 300°C still didnt move so i went to 320 and thats where it moved so i waited a few second and lifted it up, just be carefull and make a picture of all the caps around it in case u knock so off i accedently nocked 2 of but luckly i knew wher there where from thank to my picture :-)
for reballing i started at 100 for 30 seconds then went to 180 my solder past has a melting temp of 138°C thats what is recommended for emmcs , after i saw that all balls formed i let it cool of a bit then i used some isoprop gave it a nice clean as far as i could tryed to remove didnt work taht well so i heated it up a lil with 100°C and gave the balls on top die and bottum a little push and it fell right out .
gave it a nother nice clean with isoprop and picked out al the tiny solder balls that wer between the balls let it dry gave it another nice clean
after that i put a small amount of flux on the board preaheteated to with 100°C for a minute wennt to 220° for a min then added a bit more flux waited a few sec and u could se that the sat in position gave it a little notch make sure it was sitting right and then i let it cool down.
for the perfekt position i made picture of the emmc befor i took it out and set it almoast exactly in the same position befor i started resoldering