Then perhaps the boon text should be revised to make this more clear. As it stands, it says "casters." Otherwise, nongurus waste a lot of time trying to make it work for the wrong type of caster.
I would add that there may be other extenuating circumstances where it may not work. Despite the instructions, it seems that it may be more complex in some cases than simply adding the Improved Familiar feat, even for the correct type of caster.
Lastly...
Even if a draconic sorcerer can't have a "normal" familiar, having access to one that possesses some draconic angle seems to make sense. Oh well. The final word seems to be No.