@azure I had a similar discussion with a consultant about six months ago. His view was that they had a fairly good range of genetic and racial indicators for T2 and they believed that it was not too long before they could develop a screening test for it.
T1 on the other hand was, as you say, not so easy. The indications from the work done relating to the vaccine approach are that whilst the vaccine reduces the number of T-Cells that attack the pancreas, it doesn't stop them completely, or it doesn't stop whatever causes them to be created. So far it's only proven to be effective up to 15 months and requires regular injections.
There also doesn't seem to have been, until recently at least, a systematic attempt to record what had happened in the 12-18 months previous to diagnosis of type one to determine whether there are any patterns.