Hot? yes, but apparently cooler than England right now as long as you're a meter below ground in a ring around the poles (how's a constant 21c/70f sound)
this guy's website is so weird but I love the novelty of the idea and he portrays a plausible scenario for it being ultimately more habitable than Mars
"We choose to go to Mercury in this decade and do the other things. Not because they are eat, but because fuck God. Stick this rocket all the way up your divine ass. We're going to Mercury and we're going to live there!" -