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
Potentially shorter than Mars since mercury's orbit apparently brings it closer to every other planet than any other, at some point :shrug-outta-hecks: