Shave your comment about the coasters technically is right. They are getting a brand new cheap coaster.. "Frankie's Mini Mine Train".
Kidding aside I'm OK with what they are going to do to the area. Beside the 3 brand new rides, and a SFOT relocation ride. They are reworking the whole area the mini buildings are remaining and everything is else is getting a complete makeover even the Large Play Structure. So the remodel of the kids area is going to be pretty significant change for the park.
I don't believe they are entirely using Frontier City as a feeder park. It has always been a feeder park for Over Texas. There is a lot of OKC metro resident's I know who don't care to set foot in Frontier City and have Passes too Over Texas. Now that Frontier City is back they feel their Pass has more value. They plan to visit Fright Fest this year and HITP. The way Passes work this time around compared to back in 2006. It's a win for Frontier City. It will be interesting how the membership works at this park in 2019.
Future attraction wise I'm not worried one Six Flags only leasing the management rights to the park. The one that will fit the bill for new rides will be EPR out of Kansas City. EPR is financial backers of Top Golf, Schlitterbahn Water park Resorts, Several theme park and amusement parks. They will make sure to continue investing into their parks.