Hello,
it is not just about removing the extensions filtering that prevents you from selecting a *.ifc file.
It is also to modify a chunck of datasmith runtime code so that you can use IFC library to read ifc file at runtime and create assets, probably allow UE to package with the IFC reading library. Those are not easy changes.
In 5.1 we are refactoring the import process that allow more homogeneous framework.
That will open the road to runtime import to CAD including IFC. As said earlier if all goes well such feature will be beta in 5.1 and you will have to wait more version to get a reliable feature for CAD runtime import.