Can you be a little more clear? How doesn't it work? Do the modpacks show up to select at all when you launch MK8 after launching SDCafiine? Or do the modpacks boot but then the game freezes when you launch a track?
Cuz if your problem is the latter, the solution is to just reload and try again, it's a little finicky, but once a race properly loads, all races seem to load without issue in that play session. If the modpacks aren't appearing at all when you launch the game, then that means you have not properly placed them exactly where they need to be on your SD card.
While I'm here, to anyone interested, I know this is long delayed, but I do have a sizable update coming that will replace all the remaining old but retextured tracks in Invitational and 2nd Tour with brand new tracks to Mario Kart 8. Hopefully I'll get that out by the end of the week.
EDIT: Said update is being held off on, as a proper stage expansion for the Wii U that has been available through CTGP Cafe is now open to be modded, so I'm actually moving into that environment. Early results are great, however, not everything functions yet, so this update may be awhile yet. I might push a finale non stage-expansion entry in the coming days, but I'm very excited for properly expanding the stages now