In exchange for a couple of late 1st rounders, Detroit sent one of the top QBs in the league to another team. The guy they got in return is a sizeable step back from Stafford. And how long it will be that they are able to get another guy as elite as Stafford is unpredictable. Goff is probably good enough to keep the Lions in the mid-round selection group which means they aren't going to get a shot at the hot college QB prospect unless they give up all the draft capital they received for the trade with the Rams and then cross their fingers that a team with a top 3 or 4 picks WANTS to trade down.
But..... a team can get lucky as the Rams did with Warner, Seattle did with Wilson and the Pats did with Brady.