High power incandescents used to use E40, while this lamp is obviously designed to replace one of those...
Must be quite rare by now then. I suspect the CFL was made as "energy saving" alternative for new fixtures rather than retrofit for old ones
And besides, you could install a ballast box on the cable, or a ballast box that the fixture plugs into as is (using pulse start lamp, so that plugging the fixture in without the ballast won't cause lamp explosion)
But the ~2..3kg would be really too much...
They can hold much more than that. You can lift a 5kg+ light fixture by the socket or by the lamp screwed into it, if the lamp itself won't break