The starting center (Nick Martin) was lost for the year before the season started and the starting right tackle (Derek Newton) was lost early on. He tore the patella tendons in both knees and is doubtful to return this year.
The back up center played well and could help at guard this year if Martin returns healthy (likely). One of the guards (Xavier Su'a-Filo) was, in his 2nd year in 2016, improved during the year and really turned it on towards the end of the year.
The Texans drafted a tackle in the 4th round this year, but he will be a project and is not expected to be of any help for some time. Right tackle will be a work in progress, but there are a couple serviceable options and hopefully someone steps up.
On a positive note, Duane Brown is at left tackle and is an all pro. At lease the "blindside" is covered.
The line, as a whole, did improve over the year in 2016 and could be, at the least, less of a liability this year.
The strength of the team is definitely defense so the QB can be more of a game manager. That bodes well for DW4 to have time to get acclimated and not have to carry the team on his back early on in his career.