I doubt it would ever be even closely comparable to grassfed meats. One only has to look at the dire quality of astronaut-food to see that humans could have done much better by now, if they really had tried. Plus, one of the reasons why wild game is so superior is that wild animals do lots of exercise, something one could not replicate in a hydroponics lab etc.
It's not fair to compare astronaut food to lab-grown meat. There are severe weight restrictions on what can be taken into orbit.
Eventually vat-grown meat will be do-able on a small scale, very cheaply, at home. At this point all you'd have to do is make sure the meat was getting all the necessary micro-minerals, etc., and it's going to be just as healthy as grassfed.
Getting the meat to have the same chemistry as grassfed is simply a matter of--yes--chemistry. Different chemicals/nutrients/etc. are associated with epigenetic triggers in cells. Figure out what those triggers are, and you can change the cells into whatever you want.
Yes, it will take time to get to that point, but probably not more than a few years. Meanwhile, the cost of grassfed meat probably won't go up too much, because the masses will be so willing to buy the cheaper vat-grown meat. When vat-grown meat gets to the point where it's as good as grassfed, then it will be safe to switch to it.