Is there any reason not to drill holes and use m5 rivnuts in a steel frame with no bottle bosses instead of getting them added by a frame builder? Not arsed about aesthetics...
Nope, provided it's not a top end steel frame made with wafferthin steel, in which case strengthening pieces around the bosses might be a good idea. But if it's just boggo steel, rivnuts are fine. Put a blob of epoxy on them when you insert them to help prevent them spinning in the future.
Is there any reason not to drill holes and use m5 rivnuts in a steel frame with no bottle bosses instead of getting them added by a frame builder? Not arsed about aesthetics...