on approach go directly to flaps 5 on 737ng
 

Besides possible asymmetry at less than flaps 5 is there any other reason why one cannot skip flaps 1
Also the airspeed indicator indicate the flap position,where does it gets its info.

Does the airspeed tape indicate the flap position? I thought it indicated the flap lever position?

Given then nature of flap 5, I imageine going direct would significantly increase the baloon effect. Never tried it and probably never will for the asym reason alone.

I think is impossible due to the mechanical gate of the flap lever.

You will get a few personal opinions but if you want facts then write directly to Boeing in Seattle. Include your recommendation and maybe Boeing will think it is a good idea.:rolleyes: Boeing would undoubtedly looked at that during initial test flying and come up with the current recommended procedure. Stick to that procedure and you have covered yourself.