I'd personally prefer it to work similar to hellstone, by using the same bombs/ rockets it keeps things simple and intuitive.
It would suck to loose the use of more aesthetic bombproof blocks, but at the very least there would still be good options at each stage of progression for practical use. I'd love to see a way of bomb proofing normal blocks without affecting their appearance, maybe something like a coating.
This could be a bit off, since it could make collecting on stage ore too easy, I figure having it set after the ores progression tier with a check is best. Same reason why I like how hellstone works with the transition into hard-mode.