Here is a direct quote from the FCC website regarding the LPTV stations that also broadcast on the 87.7 FM frequencies (and sometimes 87.9 FM) nationwide...
The FCC has established September 1, 2015 as the date for the termination of all analog low-power television service. After that date, analog television will no longer exist in the United States.
( Soure link
That means in less than two years, the station currently calling itself WKQX-LP will no longer be around. Even with it currently working, a huge portion of the market cannot even access that station. That is not a sound business investment for a company like Tribune Broadcasting, which is currently being run by some very sharp business people.
There are much better options open to Tribune Broadcasting than just 87.7 FM. A station like what is being planned for WGN-FM (or whatever call letters they end up using) needs to be on a strong, clear signal that can reach the maximum amount of listeners. That gives them the best chance at high ratings, and more importantly, the best chance to bring in high revenues, which a 24/7 live talk station absolutely needs to survive. 87.7 FM does not deliver that potential for Tribune Broadcasting. Randy Michaels' Radioactive LLC can keep paying the monthly bill to Venture Technologies so he can keep his little LPTV/radio playground.