Tokyo Drift felt really out of place in the timeline. Nothing seemed to add up because it was assumed the events occurred either completely independent of Dom's realm, or perhaps directly after 2 Fast 2 Furious based on Dom's appearance at the end of the film.
The writers did an amazing job re-introducing Han into the big picture by giving him a small yet effective role in Fast and Furious; despite his short time on screen, Han is established to be a valuable friend and associate of Dom's as he is an incredibly skilled driver at the very least. Han reprised his role in Fast Five and in Fast 6 on a much larger scale, establishing a relationship with Gisele. The events in Fast 6 now opened the door for Tokyo Drift to entire its place in the timeline; Han leaves the crew to pursue his own personal affairs after the death of Gisele.
In Tokyo Drift, Han establishes himself and takes on the "Dom" persona of the street-racing and crime scene; he's well respected by friends and enemies and only drives competitively when he truly needs to. Backtracking to the important exchange between Brian and Mia in Fast and Furious - Dom is respected because he lives by his own code. His strong and influential presence effects those around him - Brian and Han included. This is made evident by the conversation Han and Sean have at the top of the building, when he explains what he finds important (trust) and why he drifts. Han, like Dom, has established his own code.
In later events in Tokyo Drift, Han races DK in the streets and dies in an apparent racing accident. However, it is revealed at the end of Fast 6 that it was no accident; Shaw's brother Ian was behind the wheel of the car that struck Han, killing him as revenge for the death of his brother, which Han was partially responsible for. He phones Dom and lures him out to Tokyo, which likely explains Dom's cameo appearance at the very end of Tokyo Drift.
So, Tokyo Drift now has a clear time-stamp in the entire franchise. The events of Tokyo Drift happen after Fast 6 (perhaps not immediately after, as Han would have needed some time to establish himself in that city), which tells us that at least some of Fast 7 will be set in Tokyo. Some other questions that come to mind is if anyone in the Tokyo Drift realm will be included in Fast 7; the notable figures are obviously Sean, Twinkie, and Neela, but none of them really have the chops to hang with Dom and his crew.
Perhaps the most exciting prospect of Fast 7 (to me) is that the dynamic has been completely changed; Dom and Brian have been depended on to apprehend a villain or steal a lump of money, but this time, they are being hunted by Ian Shaw (Jason Statham), which shows his ruthless personality by stalking and killing Han.
