I would think that repeal of the 1986 law would be mandatory for the repeal of 1934 to be of any value, as the 1986 law bans the civilian use of class III receivers manufactured after 1986. BUT if you are LE, military, or licensed with no transfer allowed, you can participate. Effectively, the 1986 law banned machine guns, by placing an exorbintant value on them and leaving the average citizen hopelessly outgunned by the potentially tyrannical Government. The 1934 Act taxed them precipitating over time the exorbitant prices of today.
Actually, MGs weren’t all that expensive before the 1986 end of new registrations. It’s the scarcity of a fixed set of legal MGs, plus all the years of people buying them up as collectibles and investments, that have made them expensive...and unfortunately I’ve no doubt that many current owners of pre-86 MGs will oppose repeal of the Hughes Amendment, so as not to lose their investment.