Zardnaar
Legend
So eliminate all the optional rules, implement the "gritty rest" rules. Heck, if you want to take Gygax's opinion to heart eliminate cantrips. Anything else you wanted to pull in from previous editions (wands with n number of charges ever, scrolls, etc) is easy.
As far as being easier to mod that's not an opinion that's going to be shared by everyone. I find 5E incredibly easy to mod, even though I don't do it much.
But, like I said ... separate thread.
2E has a lot more toolbox type books and settings.
The griity rules in 5E actually fail they just stretch out the 6-8 encounters over a week instead of a day.
It doesn't really change the baked in encounters, rapid healing, high powered PCs etc.