Bottom line, for the average person who doesn't have stacks of dollars or proper connections it's impossible to cross overland into Myanmar. Flights were 1000 yuan last summer to Mandalay or rangon.

You can explore Shan state extensively from the Myanmar side as long as you don't get too close to the border areas.

This summer when applying for a Myanmar visa at the kunming embassy I was informed that crossing at Ruili is forbidden and had to show plane tickets to obtain a visa. On the Myanmar side I got as far as Lashio before being told that further travel was not posdible. It may be possible if you have private guide and a stack of dollars but not using public buses