As currently worded, you can take two additional turns if you legend rule then sac the Nexus.
Not sure who is hating on tri-color. Gold sets have been the most popular and best selling sets historically. They are doing them more often because they continue to be more popular. They used to do them more sparingly, afraid that they might overdo it, but doesn't seem to be the case. The majority of players are not getting tired of gold and multi-color stuff. They like doing powerful and splashy things, which you get with gold cards.
With all the mana fixing that will be available, it won't be hard to run 3 colors. BUT, you need to make sure you have one main color and two 'splash' colors that you don't need till later turns. Plus, avoid double colored mana in your splash colors. If you are Bug (mainly black, splash U/G), for example, aim for being able to cast any spell in your deck with one forest, one island and XX swamps in play.
There's a few exceptions, especially if you run green with Caryatids and Coursers, but that rule of thumb isn't for the players that looked at my advice and said 'that's not quite true'. It's for the newer players that get a little too greedy with mana bases in these sets.
