Yep, I got the Elegant Desk! I love the Elegant Desk + Chair, but I never got around to getting the chair before I reset my Alpha Sapphire game. I'll probably get them again soon to really polish my Secret Base.
A little trick for the soot: go into the soot collector's house, step out and get soot from the pile outside his door, then re-enter his house and repeat that. I got enough soot to get the Elegant Desk just by doing that for about a half hour, so just find something to watch on tv/Netflix and lather, rinse, repeat that.