I've seen people complain about the transwarp beaming last time for several reasons, one of them being "wahhh, they'll use it for the plot and then forget they have it in the next movie". They obviously didn't. Now, it's "wahhh, Khan's super blood was used as a McGuffin-esque plot device to save Kirk, and woe to everyone if they pick it up again in the next installment. They did the same with the transwarp plot point, how dare they have continuity!".
Seriously, what's up with that? Either you hate it that stuff gets introduced and never mentioned again, or you hate the exact opposite. You can't hate both. It makes no fucking sense.
There's no pleasing some people.
I for one am uber happy they kept him alive, and I hope he and his awesome magic blood get mentioned again in the future. I even hope it becomes a plot point, because the moral implications alone of harvesting someone's blood are incredibly complex.
It was an obvious plot device that (unlike Spock's resurrection) everybody could see coming a mile off. It definitely impacted on the emotion of the scene, although I shed a tear when Quinto's facade cracked. I also laughed out loud at the 'homage' to TWoK. Fair play, it was hilarious.
My issue with transwarp beaming is that I simply don't see how it could work the way it does in the movie without a serious amount of collateral technology (how can the signal travel faster than a subspace signal - which can take hours or days to reach its destination; how can it travel over longer distances than a subspace signal without specially designed subspace relays (Scotty used standard Federation communication relays in the comic and Harrison I assume must have hacked Klingon communication relays but a transporter signal contains a hell of a lot more data than a subspace communication); how can the annular confinement beam retain the integrity of a signal without something extra to power the beam; since scanners don't have that kind of range (quite often they don't even detect a ship in visual range) and they can't even beam up a person who is moving too much, how can a person not die if they are beaming over light years without a receiving pad to aim for). It should be a death sentence and it irritates me that they hand waved that away with a 'ooh this is soo dangerous but we'll use it and succeed anyway' line.
They can easily use the serum again but it will depend on the plot whether it works. A throwaway line, "The serum didn't work this time Jim.' is all it takes.
I find the casual disregard for inter-stellar distances far more annoying than the serum. No longer will it matter if the Enterprise is the only ship in the quadrant when all the other ships can travel there in less than a day. Why dis Spock even care that the fleet was in the Laurentian system - he could have sent a subspace message to Feceration outposts nearer to the fleet and given them half an hour to turn up.