said by Andy from CA:IMHO the best solution is to allow cable/FiOS customers the option to zoom or not by putting that option in the boxes (as it exists in OTA STBs) and providing all 16x9 channels in 16x9. Just IMHO, YMMV.
That's the problem though. If you are sticking in the SD domain, you CANT'T provider 16:9 content as 16:9 content. You can only provide it as a 4:3 frame with 16:9 content letterboxed. If you provide a zoom mode on that for 4:3 content, then the 4:3 content would only have like 1/4 the resolution as they should.
The only viable solution to provide from the STB end is to eliminate the SD channels altogether and give everyone an HD STB, even if you are using it with an SDTV. That way, the downconversion happens at the box and you can provide a centercut mode like the OTA STBs do.
So, it's more than just providing options in the STB. You have to change the type of STB that SD users have and you have to make changes at the VHO to eliminate the SD channels.