In the past 5 years, 6 teams with 6 wins or less the previous season have made leaps of 6 or more wins. They are:
2001 Patriots - 11-5 from 5-11 (Super Bowl Champs)
2001 Bears - 13-3 from 5-11
2001 49ers - 12-4 from 6-10
2000 Eagles - 11-5 from 5-11
1999 Rams - 13-3 from 4-12 (Super Bowl Champs)
1999 Colts - 13-3 from 3-13
So it's fairly likely that one of the 13 teams in the NFL that finished with 6 wins or less will make a big jump and emerge as a contender. That gives the Texans about 13/1 odds of being that team. Vegas likes the Texans even more, giving them a 10/1 shot at winning the AFC South. So while it's not impossible for the Texans to finish at 12-4 (not with the type of talent they have at the skill positions), I wouldn't bet the farm on it.