I really don't have my hopes up and in my heart of hearts, I believe this is just a marketing campaign.
That said, three things of interest are happening here.
1) In order for an NBA franchise to change it's logo and/or uniforms, it has to get approval from the league office ONE YEAR in advance. Dabods is right that these things tend to be announced well in advance but in this case, the team may not have had this planned for 12 months or more because...
2) This isn't a new logo or new uniform and so I wonder if such rules apply to this. The Sixers aren't putting anything new out, they're just using the old stuff again.
3) Ed Stefanski took over as President in December. He's not only the man making the decisions for this franchise on the court but he also has say in off the court matters. I don't think it's a huge stretch for him to say that he wants the team to use to the old look for now especially when you take into account that he was a huge fan of this team during that era.
Again, I think this is just a marketing ploy but given the events that have transpired over the past 9 months, I don't think it's that insane for the switch to happen. Hell, I've seen more of the old logo and uni's in the past month than I have in the past 15 years combined.