There are significant differences between the vaporware P210 American and the older design, all most likely chosen to reduce production costs, which is why the original estimated retail was half what the older model was. There's quite a few posts out there detailing the differences, but the largest is changing the barrel lockup system.
As to when, I wouldn't even want to guess, might not even be this year. These were shown off at the 2016 SHOT show, Adam Painchaud, VP of SIG academy is on video Jan 21, 2016 telling an interviewer they are "shipping now". There's also the NRA Annual Meeting video interview from May 28, 2016 with Tim Butler, SIG Pistol Product Manager stating that all four proposed models would be in stores by now, with the last model the compact carry arriving "right around 2017". At SHOT this year they were telling people they should be in stores by April/May.
So if you believe SIG they should have hit stores by February 2016, with 4 models out by January 2017, since we're here in April 2017 and they are still vaporware I wouldn't put much weight into anything SIG said until you see them for sale in stores. It does make you wonder though what the problem has been getting these to market, or if it's just fall out from the government contract push. In addition the stated retail over those original interviews has gone up $300-$400.