Lords of Time. Basically, ways to control time and harness it to your advantage. Given the power of this mod, it would definitely be endgame.
Temporal Generator: Utilizing the raw power of time, you have created a machine that can generate electricity (RF, maybe) as time particles, chronons, flow through it. The faster time goes by, the faster it generates power, so using this in an eternal day/night world would be pointless, but a fast time world would allow the generation of more power than the Overworld.
Chronon Concentrator: Using a specialized filter created from the heart of a dead demigod (the Wither), you have discovered a way to concentrate chronons into physical form, creating chronon dust. Uses massive amounts of power to control and stabilize the process. Creates a 3 cubic meter localized time dilation effect, slowing down things nearby by a factor of eight.
Infused Temporal Alloy: By mingling chronon dust with the space-warping power of ender pearls and applying it to a gold substrate, you have created an alloy that pulses with the power of time itself. This is the substance you will need to further your experiments in time manipulation.
Static Chronon Field Generator: This machine is your first stop, allowing the complete cessation of time within a given radius. The power draw is the stuff of legends, but its uses are many and varied. Trespasser prevention system, mob demobilizer, buffer zone, and more. This machine, however, seems to have only a single flaw: complex lifeforms (such as players) aren't completely stopped, only drastically slowed down. It seems that they possess a stronger local temporal field than lower forms.
Emergency Temporal Shelter: With a little work, you've found a way to bind temporal energy to your life force, creating something of a fail-safe system should you be in danger of dying. While this item is in your inventory, should you ever reach less than two hearts of health, this item will activate, sheltering you within a static time field for a short time (enough to regenerate to half health normally). This item can only be used once, however, and once used, it shatters into uselessness.
I've ideas for plenty of other things, as well, like a machine that uses a localized time disruption to form an impenetrable, invisible barrier around a given area, grenades that slow time, chronon accelerators, chronon-infused power armour, stuff like that.