I wouldn't balance around PVP.. it can create unforeseen and negative effects. Although I do hope this game will allow for some open world PvP (like corps fighting over territories), but dear god don't try to make an e-sport out of it...
Not so sure about modding.. developing proper interface for quick modifications is a must have anyway- you want to have a quick and easy way to shape your game a you see fit, it's a no brainer...
BUT, opening it up for all people is not so wise. I could get behind visual mods like in Warframe...
Bad news: we are pretty far from something tangible...
Good news: UE allows for some ridiculously rapid prototyping so when the actual work WILL begin we shall see effects of it pretty soon.
Worked with UE for quite some and I'm very happy they are betting on it.