I have used a several of my AR's for 'poodle-popping' - (coyote to ground hogs to etc.)
I don't know that I would use one in 5.56/.223 for 'deer-sized' game, but I'm sure there are a few out there who have and swear by it.
For that size of game, I do have uppers in 6.8SPC, 6.5 Grendel, and 30 Rem. All have worked well.
For BIGGER game, move up to 7.62 (.308), .458 SOCOM, or even the .450 Bushmaster. Olympic Arms is making uppers in .338, also.
If this venture works out for Mossberg, I can foresee them dabbling into a 7.62 model in the future. All depends on sales.
I haven't seen the formal 'technical spec' sheet on these yet, but they look like standard receivers. That being the case, one could buy any of these new Mossy's and assemble or buy a few different upper assemblies to fit one's needs
I wonder if Mossberg will offer accessories, and if so, what kinds.