1) Great Bishop of Geneva! Would Sunday Laws Forbit Sabbath Keepers to Buy and Sell?, 2) New blog on the kid John Cornwell's Incompetent Fan Club Claims Vatican went Nazi
Since my dad has been a Seventh Day Adventist, and since I am a Catholic and in favour of Sunday laws, I can hardly avoid the question.
In the Middle Ages, there were of course Jews who kept the Sabbath living in pretty many towns. Even if they were expelled from one town or even country (like Pope St Pius V expelled them from the Papal States in 1569, I just learned, and gave them 90 days to comply - when I think 100 km or 65 miles would have been enough to be outside its then borders) there were other countries receiving them, and so there were always Sabbath keepers - if they like to call themselves such - among Catholics who reckon the Resurrection as a New Creation and therefore as superceding the Sabbath.
If EVERY businessman without ANY exception were required to close on Sunday and be open all other days, then indeed a Jewish or Seventh Day Adventist business owner would be in trouble.
That was not the case in the Middle Ages. Typically this or that trade would be reserved to guilds, every guild was Christian - as in Catholic (up to Reformation) - but every town decided which trades that applied to and so in every town which had Jews, there could be a trade or two or three where they could perhaps even do business on Sunday - within their part of the town* - but certainly close on the Sabbath. They cannot say that doing business on every non-Sabbath day is required, even if they think working every non-Sabbath day is required. There are works that can be done at home.
So, no, going back to the Medieval system would not be what a Sabbath keeper could in any justice or with any plausibility construe as a fulfilment of Revelation 13:17.
UL of Nanterre
* As in Carpentras, where a certain man was bishop before he became Pope Julius II. Be it noted that his enmity against the French was not inconsistent, since Carpentras in his time did not yet belong to France.