Currently -- *.mq4 files created by EA Studio can be imported by EA Studio, and *.mq4 files created by FSBPro can be imported by FSBPro. Importing a source file (*.mq4) is not easy because it has to be parsed. In order to accomplish this the source file must conform to a specific format.
Since both EA Studio and FSBPro are Popov's applications and he is familiar with the format of the source code then, perhaps, one day EA Studio-generated source files can be imported by FSBPro and vice-versa. However, I'm not sure this is such a high priority. Also, because of the different features of EA Studio-generated source files and FSBPro source files, then it may not be feasible.
As for importing 3rd-party source files -- no way. A source file is simply a text file with a bunch of lines of code. There is no way for a software application to read, parse and interpret the meaning of the lines of text of an arbitrary file. That would require software that was skilled in AI.