I agree, it is sad. :(
There is hope, however! I opened up one of the .m5f files that is saved from UI Flow to learn that it is a hybrid json/xml file with all the blockly code represented in XML. I'm thinking of working up a simple script that could be run in browser to parse this data and allow you pull single blocks and merge them into another file.
The concept here is that you upload two files (library.m5f and project.m5f, for examples sake) and then you can pluck whole blocks from and to either file. This way your great new invention from project.m5f can be added to your library and your great work from the library can be added to your project.
It will be simple, dare I say crude, to start with but should help. Also, I did tinker with making a custom .m5b file and it's not that hard but not quite the same as having a pre-built set of routines you want to use all the time. I'll post more info here once I have anything worth playing with.
