Trump's Thursday proposal is generally regarded as disastrous by Beltway immigration patriots and it's shifted their assessment of the odds: to Disaster 50%-Deadlock 50%. Hope of getting actual patriotic immigration reform through this Congress seems to have evaporated.
Why is Trump doing this? The most obvious explanation—he really wants a wall, among other things. And in fact he's surprised sensible observers by how far he's moved Democrats on the issue e.g. Democrats should give Trump his wall if it means Dreamers can stay, by Victoria M. DeFrancesco Soto, NBC.com, January 24, 2018.
What will happen? As usual with Trump, no-one really knows—but we've been here before, many times. Plus the Democrats are reacting with their usual arrogant intransigence—which is maybe what Trump was plotting all along.