Was that overtly provocative?
I don't think anyone outside the Daily Mail's readership base expected anything different. The rights of citizens on both sides will be guaranteed, there's too big a cost not to do so. It's just that no side wants to blink first. I also don't think NI border was ever seriously considered a domestic matter to resolve and was always going to be a key debate with the EU (May's letter accepted as much).
The real area of push back will likely be the exit bill, mainly because the government won't want to look weak but it'll inevitably be settled for less and over a longer period of time. Don't get me wrong, this whole negotiation process is an utter waste of resources and effort which ultimately will harm the UK more as it's got fewer man hours and resources to spare but the impact on a few headline articles seem overstated to me. For instance, there's already indications that the EU will be open to a transition deal provided it's supervised by the ECJ and subject to further payments etc. Now that may not play well with 'hard' Brexiters but there's very little opposition to the government at the moment so they'll be able to ride it out.
Also -
UKIP's Suzanne Evans told a BBC Question Time audience that Britain "should not pay a penny" when it leaves the EU, and prominent Tory Leaver Iain Duncan Smith outlined a UK claim to a share of EU assets that he suggested would be more than enough to eliminate any UK liability.
No one listens to these two idiots. Their political capital is non existent.