(I think you mean bootstrap5_block_rules.js.) As you say, the code is clear and it wouldn’t be difficult to create similar blocks. Having a corresponding ‘user’ file (which wouldn’t get overwritten) would be a useful feature and probably not too difficult to implement. However, it would probably be quite difficult to create a UI to create these templates - particularly if the code were validated and the resulting blocks were only allowed to be inserted to maintain valid HTML etc. Also, creating an .svg file would be a bit of a fiddle (although obviously it could be optional).
I would prefer the implementation of a related feature request, which has a lot of votes and would probably get more if it were more recent (it’s almost 4 years old).
There are several similar requests, including this one and this one.