For balance here's some of the stuff that is coming for EU migrants:
"We want EU jobseekers to have a job offer before they come here and to stop UK taxpayers having to support them if they don’t."
"We also want to restrict the time that jobseekers can legally stay in this country. So if an EU jobseeker has not found work within six months, they will be required to leave."
"Stronger powers to deport criminals and stop them coming back…and tougher and longer re-entry bans for all those who abuse free movement including beggars, rough sleepers, fraudsters and people who collude in sham marriages"
All of these things could have been done under EU law, and as such will probably be implemented before the final Brexit. Most had already been introduced. The four year ban on in-work benefits for migrants that was also proposed will now not go ahead until at least after Brexit as it required the EU to change their rules and they have said they won't.
There's a good summary of the legalities here. A key pont is this:
EU law only grants a right of residence for more than three months to those who are employed, self-employed, and economically self-sufficient as well as their family members.
Economically self-sufficient means a threshold can be set.
That threshold is set at £153 per week. That means anyone who earns, or has recently earned less than that, is not defined as a 'worker' for the purposes of in-work and out of work benefits. They are not deported, they just won't get the dole if they lose their job. It is not a stretch to suggest this could also be used as a threshold for the second policy above - that those not earning at that threshold for a period of six months could face deportation. This could probably have been implemented within the current EU rules, and if not history shows it would certainly be up for negotiation, as no doubt would the level the threshold was set at. The EU are quite happy to throw poor migrants under a bus when it suits them.
In summary, EU migrants who are poor were fucked, Leave or Remain. So what everyone's arguing about now is the more financially secure migrants. Any attempt at deporting this group would not only destroy the economy, but would turn the UK into an international pariah with very real consequences - what other country in recent history has embarked on ethnic cleansing of working, possibly property owning minorities on this scale? It would also require a massive and very violent state infrastructure that just isn't there. In fact this scenario is no more realistic then a scenario in which the UK remained in the EU but decided to deport all EU migrants anyway.
I feel really shit that people are worried, and understand that a threat like this is likely to gnaw away at you no matter how many re-assurances are offered. It is a bleak time to be poor and a bleak time to be a migrant. But that would have been the case whatever the result and the position of EU migrants is little changed. Scare-mongering without any analysis of the the actual situation is really not very helpful and I wish people would stop.