I already suggested using some game engine. And despite current issues in q-gears, the advantage would be to have the "engine" part done for free, eg interface, scripting, sound, controls, settings, etc.
For the original intent of having a drop in replacement you'd need source code to make loading of native data possible.
To get a real impression of the benefits of an engine you should face all implemented features and there quality of q-gears with the engine of choice and see what benefits and drawbacks there are.
As for Unreal 4 I See:
+ editors (live preview, visual scripting, ...)
+ input controls (Keyboard, Gamepad, Oculus?, ...)
+ settings screens (not sure what is required to get them though, ogre has only the minimal rendering settings window)
+ platforms (win, mac, *nix, android, html5)
+ possible future updates / bugfixes
+ proven architecture & maybe good quality code at least I'd assume it to be
- porting efforts
- learning efforts
- native format support may not be possible