That article doesn't do a very good job explaining the upgrade kit.  It states that the upgraded S2 will be able to hash at the same speed and power consumption as the S5.... which would mean the upgrade kit would offer a whole 150GH/s over the S2.  Also, the S2 has slots for 10 boards - which are originally filled with what are essentially underclocked S1 boards.  If the article is to be believed, then what are the other 8 slots going to be used for, if anything?

I'll wait until something official from Bitmain actually appears instead of treating the linked article as any kind of source of truth, because that article smacks of just as much speculation as this thread .

we are listening and taking info but R&D team is working to make it happen as much as they reasonably can...

S2 upgrade kit uses more chips than S5, but it is the same chip BM1834.

PSU wise, original 1000W PSU should be more than sufficient. (That is the plan)  Even the slightly under-performing S2 PSU that could hash 9 PCB but not 10, would work as well.

lets wait for the R&D to say, let it open the flood gate for the sale

These are the S2 upgrade kit hashing PCB displayed in Burin, Germany and Amsterdam, Netherlands last week.