I also wonder about the long term viability of franchise mode, with it being tied to a market and server. How long will they maintain the server, no one knows, but I would expect at least that it'll be equal to the amount of time they put in full support and DLC - 3 years of DLC through 2022, 3 years of server being maintained, to carry through all of 2025. Of course, it could be longer, but I'd be surprised if it's shorter. There's also the amount of animals on the market to take into account. As player numbers drop off, which they will over time eventually, there will be less and less offerings available. Thus discouraging people to invest more time in Franchise mode...which leads to player drop off....and so the cycle will continue.
I'd honestly like to see an alternate franchise mode at that point, one that's NOT tied to a player-based market. Animals are a set price and always available, much like most other zoo games. Set price can mean by species, or it can also take into account genetics, but animals with lower stats would always be a set price, higher stats higher price...but the most important thing - they would always be available. so like....a market that's independent of a server with other players and with Frontier offering animals sporadically, but still franchise in the sense your own zoos are connected.
If that doesn't happen, and servers go down eventually, the game essentially becomes a sandbox only game. Which, isn't awful. You can make your own challenges via settings in sandbox, make it as easy or difficult as you want. But having that preset in franchise has been helpful.