It seems to me to be a good idea to separate out the traditional refereeing (pre-publication review) functions. In mathematics at least, a paper should be “true, new and interesting”. It is often easier to check the first rather than the second, especially for less experienced researchers.  It makes sense for more experienced researchers to be asked for a quick opinion on how interesting and new a paper is, while more junior ones check correctness. This has some other advantages: if it becomes widespread, authors will have an incentive to write in a way that is understandable to new PhDs or even PhD students, which will probably improve exposition quality overall. It would reduce the load on senior researchers (I received an email yesterday from a colleague who said he had just received his 40th refereeing request for the year!) Doing a good job as a junior researcher could lead to a good CV item, so there would be an incentive to participate. Some sort of rating of reviewers will probably need to be undertaken: just as with papers that pass “peer review”, postpublication feedback from the whole community will be involved.