I don't like the look of white border cards, therefore don't plan to cover 8th and 9th edition. Maybe I will change my mind later.
As of October 2015, I have covered the blocks in Standard while I have been a player (Khans of Tarkir, Theros, Return to Ravnica, and Innistrad). I also have good coverage of Rise of the Eldrazi and Scars of Mirrodin. That leaves two incomplete blocks (Scars of Mirrodin and Zendikar). The blocks I have not even touched are from Mirrodin to Shards of Alara, inclusive. I also have good coverage of Magic 2012/13/14/15 and Origins. I have good coverage for 19 sets and no coverage for 27 sets. I am excluding reprint sets and 8th and 9th edition. If I include Battle for Zendikar, the coverage is 20 versus 27 not covered. If I add reprint sets (both Modern Masters), the counts are 22 versus 27, and finally, if I include all sets in Modern, the coverage is 22 vs 29. That means that I am almost half way there. I am not counting Time Shifted or the Zendikar Expeditions as sets.