He is a small goalie and his history suggests that he isnt good enough to be a capable starter. He has had 1 season (of 20+ games) in the AHL with a SV% over .920. At 175 lbs he doesn't have the bulk to endure the physical demands of being a starter in the NHL.
It would be a great story to be sure but its very unlikely.
Bachman is 5'10" tall but he is 20-25 lbs lighter than both Thomas and Backstrom.
In this NHL era he is a little goalie. He is 10 lbs lighter than the smallest goalie in the League...Halak.
I think history suggests that the smaller guys usually became the goalies. Its only recently that huge guys have started to become net-minders. Until modern training techniques became common, big guys were too often gangly and uncoordinated at a young age to compete in that position. But if they are trained properly, they can, and they cover more of the net. In the era of the big pads, and oversize equipment, having a 6'6 guy with pads up to his waist is an advantage. Being able to kneel down and still cover the top shelf is an advantage. With some equipment regulation changes, like we just saw at the beginning of the season, there are a number of guys struggling.
Regardless, I don't think that height and weight are as big a deal as you make it out to be. All things being equal, you'd like to have the most talented goalie with good size. Failing that, you take the most talented goalie. If he can stop the puck, that's really the only concern. He's not out there banging bodies in the corners. He needs speed, reflexes, technique and competitiveness.
Weight in the form of muscle bulk is not really an advantage as a goaltender. Carrying around unnecessary weight will slow you down and also, all that muscle needs more energy, and doesn't improve endurance. You don't see many 6'5 230 lb marathon runners. The 60 game, 60 minutes a night load of a #1 Goalie is more of a marathon than the game of a regular skater.
You see that Dubnyk is 6'6 and 210 lbs, and think that you need to be that weight to compete. But its relative. He is 2.69 lbs per inch of height.
Bachman is 5'10 and 175, which is 2.5 lbs per inch of height.
Ryan Miller is 6'2 and 175, which is 2.36 lbs per inch of height.
Jhonas Enroth is 5'10 and 166 which is 2.37 lbs per inch of height.
Really the only question is whether the guy can stop the puck. His height and weight are reasonable.