HS only at Zoom tables is probably THE BEST idea to make those games def much healthier. Bumhunting and datamining are slowly killing higher stakes action (they've already killed HU poker even at medium stakes ;(( ) and zoom tables get rid of both of them.
If someone is against is probably cos he wont be able to bumhunt anymore! Actually if you playing 4tables in 100plyrs pool you're still meeting the same players over and over again so notion that at zoom tables you cannot use reads is totally bullsh*t. It's even more challenging and interesting cos seats are constantly changing and you need to predict possible dynamic of current table really quick.
About spectators, I suggest creating just one "featured table" for every limit. Should be enough for railbirds. Being able to track chosen player due to this quick fold button might cause problem mentioned by ZeeJustin.
Problem with too small players pool to play smoothly might be overcome of doing something along the line of automatic size-adjust tables. For instance for player pool smaller than 20 instead of 6max run 4max tables until new players will come.
Oh I guess nosebleeds (100/200 +) might stay normal cos I couldn't imaging that at any time there will be enough plrs for zoom (or maybe im just too pessimistic and there is another chris moneymaker effect just around the corner ?
).
Bottom line: GREAT MOVE pokerstars. CONGRATULATIONS I'm impressed.
It obv doesn't solve problem with HU games. Of course zoom isn't an answer for HU. But there are other options like creating only anonymous HU tables. I hope that pokerstars just after finishing with zoom will put a lot of effort to bring HU games back to life too.