Anecdotes from the property agent I used in Chiang Mai hinted at the number of Ed visas issued up here. One estate she reckoned every house but one were families here on Ed visas. A pal teaches Chinese kids in Bangkok. All very wealthy. Kids are on Ed while mothers on guardian visas. Fathers tend to be working outside Thailand and visit.
Thailand have been cancelling student visa that were dodgy or people not attending classes. I know that 3 Universities in Chiang Mai had 4000 cancelled recently. This 10k seems to be the whole of the country. In the case of Chiang Mai many were cancelled 3 or 4 months ago. It was only when people went to immigration ie 90 day report etc they found out. Just shows they were not attending classes or they would have known. In general the noises coming out of immigration seem to be there are plenty of visa types available now. Get the correct one and abide by its conditions. In the past the Ed was only option for under 50's really. Now with the DTV they have a much better visa.
You have been granted a Tourist Visa. It looks like they will not process your DTV until it's canceled (or expired). If you do not want to wait till expired contact the Embassy in Japan and ask them to cancel the visa.
Not heard of one. Let us know how it goes though as the info will be valuable to know. Good luck and hope it goes well. With many immigration items a scouting trip to ask requirements often helps.