I still don't know if Kubiak will keep 3 QBs or just 2. I heard somewhere, but I don't recall where (senior moment), that Kubes plans on keeping the 53 best players he thinks will help them win. I take that to mean he is going to pick players, regardless of position, that would normally only make the PS or possibly cut, but they're good on ST. In other words, instead of having a 3rd QB standing around all the time, he might carry an extra RB or LB that he knows is good on ST. This is just an example. It could be any number of positions that they evaluate this way, although 3rd string QB seems to be one of the most obvious positions.
As for Porter, I think one of three things will happen, and alot is depending on how, or even if, Pickett plays.
#1 Pickett gets to play and he does great. Texans decide to keep him as 3rd QB and put Porter on PS.
#2 Pickett gets to play and does poorly or maybe never gets to play. Texans decide to cut Pickett and make Porter their 3rd QB.
#3 Texans decide to go with only 2 QBs, cut Pickett and put Porter on PS.
There might be more scenarios, but one of these three I think is most likely to play out. And I think it will be #3. JMHO!