I don't think it's necessarily all that bad of a thing,
provided you keep somethings in mind along the way which could a long way to help offest many of the reasons give for not concentrating on goal now. So, in no specific order, my suggestions/input:
* Be aware that there are many coaches at the mite/squirt level who would also be enthusiastic about finding a kid who wanted to play goal all the time. Why? Because they are hard to find at that age and most teams struggle to find goalies. Having a player who wants to play makes the coach's job easier and he doesn't have to worry about rotatating players in net (some who may not want to do it). Most young players are more interested in scoring goals than stopping them. Bottom line - take that coach's enthusiasm with a grain of salt.
* Find out about the person(s) running the goalie clinics (qualifications, frequency, etc.). Many times such clinics/goalie coaches fail to materialize, aren't as frequent as expected, or aren't led by a qualified coach. Ask what type of drills the coach will run in practice and make sure the drills do more than treat the goalie as a target. Probably more important as he gets older to have the drills mimic game situations when possible. The more engaged the goalie is in the practice the better - helps development and keeps things from being boring.
* One big risk is burnout. You can help avoid that by not having him play goal year round. But, be wary that coaches will put pressure on him to play on spring/summer teams as they always seem to need goalies.
* Encourage him to play other sports in the spring & summer. Will help fight the burnout issue and will allow him to develop other muscle groups and athletic skills. Soccer is good cardio workout and can help with footwork. Baseball is good for hand-eye coordination, as is lacrosse. Let him skate out playing inline/roller hockey.
* Another risk is repetitive use/stress injuries. Playing one sport, especially one position, all the time can cause the same muscle groups & joints to be used far more than others. Another good reason to play other sports. Check with a pediatric ortho doc and get their input. Goalies are especially prone to hip & lower back problems.
* Don't ignore the importance of skating & puck handling skills. Many times I've seen younger goalies not worry about that since they are in goal all the time. Encourage him to skate out frequently, be it at public skates, drop-in hockey or on roller blades around the house. Encourage him to work on his stickhanding with a ball in the driveway.
* A big part of playing goal is the mental aspect, both the mental toughness and the game situation awareness & anticipation, especially as he gets older. One benefit to skating out on occasions is that the goalie can see the game from the skaters perspective, which can help with the game situation awareness (begins to think like a scorer). If he's not skating out, take opportunities when watching games (live or on TV) to talk about how the teams set up plays, back door, stuff, etc.
* The toughest thing for young goalies is often times the other players & their parents are new to the game. Consequently, the goalie tends to get more of the blame when a goal scored, and as the goalie parent don't be surprised when the other parents turn and look at you when a goal allowed by your son. Knowing this you can work with him to expect it and be prepared to keep him confident.
FWIW, my son didn't play goalie fulltime until 2nd yr squirts (but he didn't start hockey until 2nd year mite). He played other sports in the spring up thru his first year of midgets. He rarely played goal over the spring & summer (outside one goalie camp) - skated out in roller hockey. He skated out at open/drop-in hockey all the time (during the season & summer). Lived on his roller blades & was rarely without a stick & ball around the house. Not surprisingly, the strengths most coaches/scouts point out about him now as a goalie include his skating ability, his quick feet, his athleticism, his anticipation & game awareness. He was offered (and accepted) a full DI NCAA scholarship several weeks ago, and I can say with 100% conviction that I don't think that happens if he had only played goal all the time and had not done the other things.
After all this rambling, I guess my advice would be: if you approach his playing goal fulltime aware of what the risks are and actively work with him to take steps away from practices/games to offset those risks he should be ok.
'90 Goalie Dad