A few days ago, there were rumors of some recently retired LEGO Ideas sets that would be coming back but with different set numbers. The two sets are the NASA Apollo Saturn V (21309) and the Ship in a Bottle (21313). Word has it that they were very popular and would be coming back with set numbers 92176 and 92177, respectively.
LEGO has confirm that those two particular sets will be relaunching and have also given a short statement of why they will be doing it. Note that the agreements with the two fan designers will remain the same and they will still get royalties from the sales.
From the LEGO Ideas team:
The two sets are being re-launched due to popular demand, and as they had already left the market, we could not keep the original numbers. The agreements with the Fan Designers remain unchanged.
Also: one of the new set numbers matches a fan designer’s birthday. They were both very involved in the process.