Was this done with the new Eve in mind or was there some other design concept we simply haven't seen?
There's a couple reasons outside of Evelynn that I can delve into -
The strategic value of that gank path approach is the superior positioning it offers - as you directly cut off the opponent's retreat path in top and bottom lane;
Having the path with superior positioning *also* being the path with a higher cost to detect was somewhat negative overall as this led to lanes needing to be overdefensive and overward to compensate. Warding will still heavily counter this path - but the advantages of having this path uncountered will be slightly lower. There's three main gank paths that all junglers have, each with their various tradeoffs: Straight down the river is the fastest, but most easily countered. Running along with your minion wave is the slowest but most undetectable. The tribrush gank path gives you superior positioning so the decision here was whether it also needed the hide potential that it did to be a viable gank path.
Currently, if the path is uncountered - there is enough Fog of War presence for a Tribrush gank to actually slip into your near brush - this makes aggressive plays in lane fairly impossible without a ward and causes a lot of stagnation around safety.
The reason this was done for mid-lane was so that aggressive mages could have the option to 'lean' on one side of their lane for safety. Because the two towers are skewed in terms of positioning, extending the tower vision range allows them to clear the intake from side river path to center. This means that with a single ward - a mid mage can cover 50% of their lane and thus have the appropriate playing space to play aggressive if desired.