It's all about tolerances. They must be tighter for the whole stackup of parts to use full size determinate assembly(DA) like the RV-14 does.
It may be possible to re-engineer an existing product to do that but it will come with significant changes.
Just as the RV-6 morphed into the RV-7 when prepunched skins gave way to a fully prepunched kit a full size DA version of the -7 would basically be a new model.