I'll admit I haven't really kept up with the current HDA stuff, it's possibly (and from your comment, highly likely) that this has already been in place in some cases.
Two things that, IMO, need to be done to make it truly effective:
1) Stop producing any CVBS-only cameras, EVERYTHING should have a high-def output standard. Obviously not every camera manufacturer will go for this, the top-level technology promoters would need to make it advantageous to do so. And there may be a lot of edge cases where customers want exact replacement models per contracts, but at this point I don't think there are too many analog hold-outs that are in much of a position to be picky about things.
2) Market this now. It should be upfront that everything being shipped is now "high def ready". For anyone still replacing analog cameras this could be an incentive for them to use your products. In about 2 years you can switch to a marketing campaign/promo claiming "You may already have high-def cameras in your system. If you've replaced a camera in the last 2 years, chances are it supports high-def mode. Click here to learn how to take advantage of this".