...from what it looks like they are almost completely removing all the gates in the C concourse, from what it looks like there will only be 3 gates, I'm assuming they will be the international gates...
Only C52, 54, 56, 58, and 60 are being knocked out by the new terminal. C55, 57, 59, and 61 will be the remaining FIS gates that won't be touched (58 and 60 are the FIS gates being knocked out based on that outline).
It really shouldn't be an issue as the most amount of aircraft at the end of C I have ever seen is three, which was only on certain days where DL, DE, and WW arrived simultaneously. I'm not counting the time where there was a UA B772 diversion parked at C in addition to the three other TATL flights which happened this past August. BA will also not be on the ground with both DE and WW simultaneously next summer barring IRROPS. Even the CUN flights on Saturdays are spread out through the day, so usually there is only one or two aircraft parked at the end of C, then either being towed to A/B/D or departing out of C before the next arrival.
If the airport feels like they need more FIS gates, then they can convert C51 and 53 from domestic to international. I'm sure that wouldn't be too difficult of a project to take on.
Either way, this project is definitely going to help with certain issues, especially those involving the landslide terminal and customs/immigration. The airport needs more space for additional security lines and the customs level in C desperately needs upgraded.