Even in string theory, what I read is that charges are hung on the end of open strings, so they cannot exist on closed strings of bosons. But their treatment always seemed very adhoc.
Hopefully, someday compactification will solve that problem. But I think it has the be the compacticication from 26 to 10 dimensions to get a better understanding of charge.
Static charges posses a field or action at a distnce. That suggests to me that the 16 compactified dimensions still connect the end of the 10-D strings to the rest of the universe.
Then when the ends of the strings move, macroscopically at least, photons and/or EM waves are radiated. That could be the precipation of the compactified 16-D into 3-D space as waves or boson particles-photons. Afterall those 16 D are what separated bosons from fermions in the first place.
So that is what my intuition says about charge.
BTW-There is increasing interest in the 26-D universe. The literature discusses it as closed strings with tachyons and axions, and calls it non-supersymmetric string theory. But that is just not to raise eyebrows over 26 dimensions. On another forum I was given a link to a recent paper that I have not read yet. I saved the paper but lost the link. If you are really interested email me at firstname.lastname@example.org and I'll attach the paper. It's a recent LANL preprint.
I have also suggested that there may be a new kind of charge associated with axions for which like charges attract and unlike repel. Besides the expectation that nature is symmetric in the kinds of charges that exist, it provides for DUMB electrons to navigate in axion condensates, and also provides for the force of Dark Energy from Dark Matter alone, assuming that dark matter is an axion condensate. Bohmian mechanics require SMART electrons to be guided by the axion landscape.
That's not so far fetched as in super conductors, somehow Cooper-pairs of electrons flow around atom obstacles without loss of energy. So they have to both know where to go and have some kind of frictionless self-propulsion to get there.
PS If you are a great mathematician, or could become, you might consider the compactification explanation of charge as a research topic. I am not.