Whether that happens depends on getting things started. I know that a lot of things have been done quietly behind the scenes. It's going through the Birmingham-Jefferson Civic Center authority, instead of city hall directly, which helps some. BJCC will float the bonds, which cuts the UA BoT out of the financial picture. BJCC wants to package a 45k seat open air stadium, a new convention building, and general refurbishing of the BJCC complex. There are plans for a parking deck as a future add on to the complex, and furthest out of all a possible replacement for the BJCC arena that would be able to compete for NCAA March Madness duty. I'm not sure to what degree design on these is being done as a package deal, although the stadium is the first construction priority. If the bids/designs are packaged the other parts may be slowing down starting on the stadium. Keep in mind also that although in a general sense we know what is happening it has not been formally announced yet. BJCC says they are doing it, the UA BoT has approved UAB leasing it long term as anchor tenant, but things are not rock solid yet. That has been close for some time, but there are always issues, and anytime the City of Birmingham is involved, eh, there are issues. They have to argue about splitting up the graft. #TheBrawlInTheHall
It's possible, and getting more likely with each week that passes without a firm announcement, that UAB plays at Lesion Field in 2017. OTOH, the group of local big business types who stepped in to help force the return of football includes the Gorrie brothers of Brasfield and Gorrie, who built the Georgia Dome, and are currently building the new Braves stadium. In one of the meetings, UAB AD Mark Ingram kept talking about beginning to play in the new stadium in 2018. Miller Gorrie, who is generally pretty quiet, said that 2017 was doable. Ingram started talking about how long it too to assemble building materials, prep a site, pour concrete. Gorrie gave him the eye and said "Young man, we've built stadiums all over the south. When the main interstate interchange in Birmingham was damaged and had to be replaced we bid to do the job in 90 days. They said that wasn't possible. We did it in 37 days. Don't try to tell me about pouring concrete."
If UAB plays in the new facility in 2017, most likely it will not be fully completed. You'd be looking at playing surface, home and visiting sides, with the ends yet to be completed, and at less than full seating capacity. It wouldn't be the end of the earth to do one more season at Legion Field. At least the hot water works in the locker rooms now. The city installed a new Jumbotron and did some refurb on the Old Gray Lady.