Oh, I'm sure the EU believes the Bill, on passage, would be a treaty violation.  The EU also knows, though, it has been dealing with a series of UK governments (and Brain-Truss won't be any different) and their idiot constituencies that acted like A.16 was instantaneous, that it could be oven-ready today and fully baked tomorrow.  That's stupid and wrong, but we are talking about the people who voted for Brexit, so.  The EU views itself as dealing with a four-year-old having a temper tantrum at the Christmas dinner table, and it is trying to handle it without losing too much of the good china and crystal.  So while the EU undoubtedly has a strong desire to fire a formal warning shot, it knows the effect in the UK would be, "See!  Even NOW those damned snail-eaters and beer-swillers are trying to tell our Parliament what to do!"