The G2 is better than the Nexus 5 in every way from what I have seen. The only downsides are the weird button placement and the UI...and of course you have to rely on LG for updates.
If those things don't matter to you, I don't think you'll regret the switch.
I have no doubt you could ROM it with a vanilla android ROM. Or even a stock G2 ROm with LG's UI removed. It's a popular phone and should get a lot of support from ROM makers.
I had a G2 with CM10.2 on it and that was a very nice combo. Very preferable to the original G2 ROM to me.
Sent from my liberated iridium rMini LTE