I'm an S scale convert, too. (Albeit a very sporadic/inactive one... no fault of S, though!)
You're going to love its size. You're also going to like gaining about 30% more layout in a given space than you get with O gauge or for sure, O scale.
IF you want to switch, I'd recommend switching now. Your O gauge/scale stuff will never be worth more than they are right now. Besides, if MTH and Lionel really invest heavily into S scale with some great looking product, there MAY be more O scalers making the switch to S, thus even more O gauge/scale product glutting the already saturated O gauge/scale resale market.
Lastly: You're not getting any younger. If you're already nearing retirement age, waiting for a few more years just shortens the time you'll get to enjoy S scale and there's no point in it. Get started with what's available and add the stuff you like as MTH/Lionel/whoever creates and releases it.
Jump on in, the water's fine!
Andre