What is the requirement of a higher glidepath/approach angle and is this a flight safety issue?
The most important sources of noise in an aircraft (especially during landing) are the engines, the slats/flaps and the gear. An aircraft’s angle of descent has an effect on the noise experienced by people below. Steeper the angle, the less time an aircraft spends at low altitudes, which means that fewer people should be affected by higher levels of noise.

The reduction in noise (as experienced in Frankfurt airport) due to steeper (3.2$^{\circ}$) landing approaches are due to the following:


The aircraft is higher (compared to the 3$^{\circ}$ landing angle), and as a result, less noise is heard by the people below.
The deployment of flaps before intercept may also be 0.7 nm closer to the airport as the ILS intercept occurs 0.7 nm closer to the airport.
Thrust increase for a/c stabilization 0.3 nm closer to the airport; this results in lower noise. The thrust required was also reportedly lower.
Landing gear deployment is 0.4 nm closer to the airport (at the same height of 2000 ft)


The differences due to changing the glideslope to 3.2$^{\circ}$from the present 3$^{\circ}$ is shown in the following image:



Image from Experience with the steeper approach angle of 3.2 degrees - Presentation by DLR

As for safety, this system is expected to pose no problems as most aircraft and pilots are easily capable of doing this. As an added measure, the trial is only being carried out when visibility is good (Cat I) and the trial is optional (for aircraft using ILS anyway).

Some airports (like London City) have very steep landing approaches for clearing obstructions and may require special certifications and aircraft modifications.