This is actually a long comment. Concerning point 2: Here is an amusing example when the referee wanted to collaborate with the author *on the paper that he/she was refereeing*, and so contributed a two-page appendix to the paper *without disclosing their identity:*

[Real reductive Cayley groups of rank 1 and 2. 
With appendices by Dolgachev and an anonymous referee. 
J. Algebra 436 (2015), 35–60.](http://www.ams.org/mathscinet/search/publdoc.html?arg3=&co4=AND&co5=AND&co6=AND&co7=AND&dr=all&pg4=AUCN&pg5=ICN&pg6=PC&pg7=ALLF&pg8=ET&r=1&review_format=html&s4=borovoi&s5=dolgachev&s6=&s7=&s8=All&sort=Newest&vfpref=html&yearRangeFirst=&yearRangeSecond=&yrop=eq)

(Excuse me for promoting my own work...)