Why an ARG/puzzle? Hyping Sindome's much-anticipated change by creating a multi-layered puzzle is a tip of the hat to plots and city history on Grid 2.0 and earlier.Things I get sentimental about, and hope we never lose. Plus, it's FUN!
If targeted correctly, this hype might attract new players who are more likely to be into the decking archetype, and will really push grid 3.0 along and advance that aspect of the game.
Issue: target audience / distribution
I'd suggest reddit. Or somewhere you get people who like to spend a lot of time reading text online. Maybe distributing through forums on TMS / TMC would be an option?
Would probably need to rely on playerbase (not staff) to OOC volunteer their time & creativity to market Sindome.
Not sure this is actually an issue.
I guess the best way to put this is be careful what you ask for. Inviting the wrong kind of attention from certain audiences in the internets might result in a lot of additional security / data concerns for the staff.